KR100658786B1 - Analog Output Buffer Circuit Using The Source Driving Of The TFT-LCD Panel - Google Patents

Abstract

The present invention provides an analog output buffer for driving a source of a TFT-LCD panel in which an analog output buffer used in a source driving circuit of a thin film transistor-liquid crystal display (TFT-LCD) panel can be implemented using a low temperature poly-Si TFT. It is about a circuit.

The present invention implements the analog output buffer of the TFT-LCD panel with a two-stage source follower using a low temperature poly-Si TFT and one capacitor, so that the gain is increased by the two-stage configuration and the charging speed is improved within a short time. The pixel can be driven, and since the voltage corresponding to the difference between the input voltage and the output voltage is stored in the capacitor and driven again, the pixel can be driven with accurate precision without being affected by process changes. In addition, since the analog output buffer has a simple structure, the area and power consumption can be reduced, and low-temperature poly, which requires high gradation and high resolution, is difficult to implement analog circuits due to variations in process variation and kink effect. Analog output buffers can be applied to -Si TFT-LCD panels, and system-on-glass technology (SOG) can be further developed.

TFT-LCD Panel, Source Drive Circuit, Analog Output Buffer, Low Temperature Poly-Si TFT, Source Follower, Capacitor

Description

Analog Output Buffer Circuit Using The Source Driving Of The TFT-LCD Panel}

1 shows a typical source follower.

2 is a view illustrating a source follower in which a threshold voltage is conventionally compensated.

3 conceptually illustrates an analog output buffer in the form of a conventional comparator.

4 illustrates a TFT-LCD panel to which an analog output buffer according to the present invention is applied.

5 illustrates an analog output buffer circuit according to an embodiment of the invention.

FIG. 6 is a timing diagram for driving the analog output buffer circuit shown in FIG. 5; FIG.

FIG. 7 is a diagram illustrating only a source follower portion of the analog output buffer circuit shown in FIG. 5; FIG.

FIG. 8 is a diagram illustrating an analog output buffer circuit according to another exemplary embodiment of the present invention configured by changing a connection order of a P-type source follower and an N-type source follower in FIG. 5. FIG.

FIG. 9 illustrates an analog output buffer circuit including a P-type source follower and an N-type source follower in cascode form according to another exemplary embodiment of the present invention. FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to source driving of thin film transistor-liquid crystal display (TFT-LCD) panels, and particularly to analog power buffers used in source driving circuits to reduce power consumption without being affected by process changes. The present invention relates to an analog output buffer circuit for driving a source of a TFT-LCD panel, which can be implemented with a poly-Si TFT.

With the recent development of semiconductor technology, thin film transistors, or TFT (Thin Film Transistor) related technologies, have been developed, and an active LCD, that is, TFT-LCD (TFT-Liquid Crystal Display), which drives each pixel by arranging the TFT in each pixel is developed. ) Is widely used, and it is classified into a-Si TFT-LCD, poly-Si TFT-LCD, CdSe TFT-LCD, etc. according to a material used to form a semiconductor thin film, that is, a semiconductor layer.

In this regard, various studies have been conducted to achieve SOG (System-On-Glass) by increasing the integration level such as digital source driving circuit, DC-DC converter, timing controller of TFT-LCD using low temperature poly-Si TFT. It is becoming.

However, conventional low-temperature poly-Si TFT-LCD panels, which integrate several circuits on glass substrates using low-temperature poly-Si TFTs, have higher threshold voltages and lower levels than the driving circuits of a-Si TFT-LCDs made of single crystal silicon. Due to the mobility, high operating voltage is required, high-speed circuit operation is difficult, and the size of the device increases, thereby increasing the area of the circuit.

In addition, the low-temperature poly-Si TFT described above has severe variations in threshold voltage and mobility due to irregularly distributed grain boundaries, and particularly analogs such as op-amps due to the kink effect. It is difficult to implement the output buffer circuit, and to compensate for this non-uniform characteristic, a simpler source follower (ie, drain ground amplifier) form or comparator form is used instead of an op amp having a complicated differential structure. I use it.

As an example, the accompanying drawings, FIG. 1 shows a conventional source follower, which output error (V _out ) by the threshold voltage (V _nth ) compared to the input voltage (V _in ) as shown in Equation 1 below Occurs.

Thus, in order to compensate for the threshold voltage, a source follower for compensating the threshold voltage as illustrated in FIG. 2 is implemented, which is initially thresholded by the compensation capacitor C by implementing the compensation capacitor C at the input terminal. In this manner, the voltage is stored and then driven. The output voltage V _out is represented by Equation 2 below.

In addition, the source follower of which the threshold voltage is compensated as shown in FIG. 2 may function as an analog output buffer with a simple structure, but has a disadvantage in that it is difficult to apply to a high resolution panel due to a long stabilization time.

In addition, a conventional comparator-type analog output buffer as illustrated in FIG. 3 is used, which has a high speed and a low precision, but has a disadvantage in that the structure of the comparator is complicated and power consumption is high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to implement an analog output buffer used in a source driving circuit of a TFT-LCD panel with a two-stage source follower using a low temperature poly-Si TFT and one capacitor. It is.

Another object of the present invention is to configure the analog output buffer with a two-stage source follower, thereby increasing the gain to improve the charging speed, thereby enabling the pixel to be driven within a short time.

Another object of the present invention is to store a voltage corresponding to a difference between an input voltage and an output voltage by using a capacitor when the analog output buffer is implemented, and then drive the voltage accurately, without being affected by process changes. To have it.

An object of the present invention is to configure the analog output buffer used in the source driving circuit of the TFT-LCD panel with a simple structure to reduce the area and power consumption, and to implement the analog circuit under the influence of process variation and kink effect with large deviation. Analog output buffers can be applied to low temperature poly-Si TFT-LCD panels.

A feature of the present invention for solving the above object is, in the analog output buffer used in the source driving circuit of the TFT-LCD panel, implemented by a low-temperature poly-Si TFT, P-type source connected in series A floor and an N-type source follower; A capacitor configured to store a voltage corresponding to a difference between an input voltage and an output voltage of the source follower; A discharge switch which is turned on for a predetermined time to initially discharge the load at the buffer output stage; After the initial discharge is performed, a voltage corresponding to a difference between an input voltage and an output voltage is stored in the capacitor while charging a voltage to the load of the source follower for a predetermined time, or a source follower configured to store the voltage stored in the capacitor at a buffer input terminal. An analog output buffer circuit for driving a TFT-LCD panel including a plurality of switches that are turned on and off to reflect the input of the present invention.

The P-type source follower and the N-type source follower include a P-type source follower configured at a buffer input stage and an N-type source follower configured at a buffer output stage, and the output of the P-type source follower serves as an input of the N-type source follower. It is characterized by being connected in series.

The switch may include: a first switch connected to an output terminal of the N-type source follower in parallel with the discharge switch and turned off only at the time of initial discharge; A connection between an input terminal of a P-type source follower and the first switch and a capacitor, respectively, which is turned on to charge a voltage of a source follower and store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; 2 switches; And a third switch connected in parallel between the capacitor and the second switch and turned on to reflect the voltage stored in the capacitor to the input of the P-type source follower through a contact between the buffer input terminal and the second switch. It is done.

At this time, the third switch is turned on during the time of reflecting the voltage stored in the capacitor to the input of the P-type source follower, and if the output voltage charged to the load of the source follower is less than the input voltage, the P-type TFT by the voltage stored in the capacitor And increase the gate voltage of the P-type TFT by the voltage stored in the capacitor when the output voltage charged to the load of the source follower is greater than the input voltage, so that the output voltage maintains the input voltage. do.

In another aspect of the present invention, there is provided an analog output buffer used in a source driving circuit of a TFT-LCD panel, comprising: an N-type source follower and a P-type source follower implemented in low temperature poly-Si TFT and connected in series in two stages; A capacitor configured to store a voltage corresponding to a difference between an input voltage and an output voltage of the source follower; A charging switch which is turned on for a predetermined time to initially charge a load at the buffer output stage; After the initial charging is performed, a voltage corresponding to a difference between an input voltage and an output voltage is stored in the capacitor at the same time as the voltage is discharged to the load of the source follower, or a source follower configured to store the voltage stored in the capacitor at the buffer input terminal. An analog output buffer circuit for driving a TFT-LCD panel including a plurality of switches that are turned on and off to reflect the input of the present invention.

The N-type source follower and the P-type source follower include an N-type source follower configured at a buffer input terminal and a P-type source follower configured at a buffer output terminal, and the output of the N-type source follower serves as an input of the P-type source follower. It is characterized by being connected in series.

The switch may include: a first switch connected to an output terminal of the N-type source follower in parallel with the discharge switch and turned off only at the time of initial charging; An input terminal of an N-type source follower and the first switch and a capacitor, respectively, connected to each other to discharge a voltage to a load of the source follower and to store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; 2 switches; And a third switch connected in parallel between the capacitor and the second switch, the third switch being turned on to reflect the voltage stored in the capacitor to the input of the N-type source follower through a contact between the buffer input terminal and the second switch. It is done.

At this time, the third switch is turned on during the time of reflecting the voltage stored in the capacitor to the input of the N-type source follower, if the output voltage charged to the load of the source follower is less than the input voltage N-type TFT by the voltage stored in the capacitor The gate voltage of the N-type TFT is decreased by the voltage stored in the capacitor when the gate voltage of the source follower is increased and the output voltage charged to the load of the source follower is greater than the input voltage, so that the output voltage maintains the input voltage. It is done.

Another feature of the present invention is an analog output buffer used in a source driving circuit of a TFT-LCD panel, which is implemented by a low temperature poly-Si TFT and connected in a form of two-stage cascode, a P-type source follower and an N-type source. With a floor; An N-type TFT and a P-type TFT connected in parallel between the buffer output terminal and the output terminal of the P-type source follower and the N-type source follower, respectively; A capacitor connected between an input terminal of the source follower and an output terminal of a TFT connected to an output terminal of each source follower, and configured to store a voltage corresponding to a difference between an input voltage and an output voltage; A first switch turned on to charge or discharge a voltage in the load of the source follower for a predetermined time and to store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; A TFT-PCD panel connected in parallel between the capacitor and the first switch, the second switch including a second switch turned on to reflect the voltage at the capacitor to the input of the source follower through a contact between the buffer input terminal and the first switch. An analog output buffer circuit for driving a source is provided.

The first switch may be connected between a buffer input terminal and an input terminal of the source follower, and between the buffer output terminal and the capacitor, respectively.

The first switch is turned on during the time of charging or discharging the voltage of the source follower. When the voltage charged to the load of the source follower is greater than the input voltage in the previous time, the N-type source follower which is the second stage source follower is provided. When the voltage of the load of the source follower in the previous time is less than the input voltage, the voltage is discharged to the load of the P-type source follower, the source follower of the first stage, and the output voltage It is characterized in that to maintain the input voltage.

The switch may be any one of a P-type TFT switch, an N-type TFT switch, or a switch in the form of a transmission gate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, the analog output buffer, that is, the analog output buffer used in the source driving circuit of the TFT-LCD panel, is implemented using low temperature poly-Si TFT, and the analog output buffer is implemented using low temperature poly-Si TFT. In this case, it can be driven in a short time without being affected by process change, and can show accurate precision, and it is possible to drive with low power consumption with simple structure.

That is, in the TFT-LCD panel to which the analog output buffer according to the present invention is applied, as shown in FIG. 4, the M-N panel is arranged based on the pixel array 10 arranged in an M × N matrix form. The data line is connected to the source driving circuit (or data driving circuit) 40 and the N scan lines are connected to the gate driving circuit (or scan driving circuit) 50.

The source driving circuit 40 includes a shift register 41, a sampling / holding latch 42, a digital-analog converter 43, and an analog output buffer. A shift register 41 generates an enable signal in the form of a pulse for sequentially storing a digital video signal input from the outside into the sampling / holding latch 42, and sampling / holding. The latch 42 stores the scan line digital video signal sampled by the shift register 41 in the sampling latch during the time that the scan line is driven, and keeps the previous scan line digital video signal static in the holding latch at the same time. It plays a role. The DA converter 43 converts the digital video signal received from the holding latch into an analog video signal voltage (ie, analog data), and the analog output buffer 44 is configured at the last stage of the source driving circuit 40, and the DA converter In order to charge the analog data converted by (43) to the corresponding pixel array 10 within a desired time, the current driving capability of the data is amplified.

In the TFT-LCD panel, the analog output buffer 44 is connected in series with the P-type source follower output of the buffer input terminal to the N-type source follower input of the buffer output terminal, as shown in FIG. The capacitor C1 is connected between the voltage input terminal of the source follower and the output terminal of the N-type source follower to store a voltage corresponding to the difference between the input voltage and the output voltage.

In addition, a first switch S1 is connected to an output terminal of the N-type source follower, and a discharge switch S1b that is turned on for a predetermined time to discharge the output terminal load is connected between the first switch S1 and the buffer output terminal. It is connected in parallel, and between the input terminal of the P-type source follower, the first switch (S1) and the capacitor (C1), the voltage of the load of the source follower (pre-charging) and the capacitor (C1) of the input voltage and output voltage The second switch S2, which is turned on to store the voltage corresponding to the difference, is connected to each other, and is also connected in parallel between the capacitor C1 and the second switch S2 to buffer the voltage stored in the capacitor C1. The third switch S3 is turned on to reflect the input of the P-type source follower through a contact between the input terminal and the second switch S2. Here, the discharge switch S1b performs a switching operation that is always opposite to the first switch S1.

Analog output buffer circuit having such a configuration is divided into three sections (T1, T2, T3) as shown in the timing diagram of Figure 6 attached to the first, during the first T1 time switch S1, 2, 3 (S1) , S2 and S3 are turned off and only the discharge switch S1b is turned on to discharge the load in the buffer output portion. During the second T2 time, the third switch S3 is maintained in the off state. In the first switch (S1) and the second switch (S2) is turned on (on) to charge the voltage to the load of the source follower, and also stores a voltage corresponding to the difference between the input voltage and the output voltage in the capacitor (C1) Done. In the last T3 time, as the first switch S1 remains on and the second switch S2 and the third switch S3 are inverted, that is, the second switch S2 is turned off and the third switch is turned off. S3 is turned on to reflect the voltage stored in the capacitor (C1) to the input of the P-type source follower to drive.

At this time, if the output voltage charged to the load of the source follower is less than the input voltage, the voltage stored in the capacitor C1 is the gate voltage of the voltage input terminal P-type TFT constituting the P-type source follower by the difference between the input voltage and the output voltage. If the output voltage is higher than the input voltage, the gate voltage of the voltage input terminal P-type TFT is lowered by the voltage stored in the capacitor C1 to drive the output voltage while maintaining the input voltage.

FIG. 7 shows only a source follower portion in the analog output buffer circuit shown in FIG. 5, which is connected to a P-type source follower and an N-type source follower in series.

Referring to the operation of the source follower, first, when a predetermined voltage V _in is supplied to the voltage input terminal of the P-type source follower, the input voltage V _in passes through the P-type source follower. The voltage at the first node 71 passing through the source follower becomes 'V _in + V _pth '. Here, 'V _pth ' means the threshold voltage of the P-type TFT.

Then, the voltage passing through the P-type source follower, that is, the voltage at the first node 71 passes through the N-type source follower again, and thus the voltage at the second node 72 passing through the N-type source follower. _Becomes '(V _in + V _pth ) -V _nth '. Here, 'V _nth ' means the threshold voltage of the N-type TFT.

As a result, when the above-described analog output buffer is applied to the source driving circuit of the TFT-LCD panel, the amount of voltage charged to the pixel of the TFT-LCD panel during the T2 time is 'V _in + (V _pth -V _nth )', that is, the input. The voltage V _in becomes the voltage applied by the threshold voltage difference V _pth -V _nth between the P-type TFT and the N-type TFT.

In addition, in the present invention, in implementing the analog output buffer circuit, since a two-stage source follower is used, the gain is increased (Ap × An), and accordingly, it is possible to charge at a higher speed.

In the present invention, when the threshold voltage changes, a difference occurs in the amount of voltage charged during the T2 time, but the voltage corresponding to the difference is stored in the capacitor C1, and the threshold voltage is driven again during the T3 time. It works without being affected by changes.

On the other hand, according to another embodiment of the present invention, the connection order of the P-type source follower and the N-type follower constituting the analog output buffer circuit shown in FIG. 5 is reversed, that is, as shown in FIG. , The output of the N-type source follower is connected in series with the input of the P-type source follower, and the capacitor (C1) is connected between the voltage input of the N-type source follower and the output of the P-type source follower, the difference between the input voltage and the output voltage The analog output buffer circuit can be implemented by storing the voltage corresponding to the voltage, which is driven by pre-discharging rather than voltage charging.

In the analog output buffer circuit shown in FIG. 8, the first, second, and third switches are connected as in FIG. 5, except that a predetermined voltage VDD is input between the first switch S1 and the buffer output terminal. In order to charge the output load, the charge switch (S1b) that is turned on for a predetermined time is connected in parallel with the voltage terminal. At this time, the charging switch S1b performs a switching operation that is always opposite to the first switch S1.

As shown in the timing diagram of FIG. 6, the analog output buffer circuit shown in FIG. 8 is divided into three sections T1, T2, and T3 and operates during the first T1 time. The 1,2,3 switches S1, S2, and S3 are turned off and only the charging switch S1b is turned on to receive the predetermined voltage VDD to charge the load in the buffer output portion. During the second T2 time period, the third switch S3 maintains the off state, while the first switch S1 and the second switch S2 are turned on to discharge the voltage to the load of the source follower. In addition, the voltage corresponding to the difference between the input voltage and the output voltage is stored in the capacitor C1. Then, at the last T3 time, as the first switch S1 remains on and the second switch S2 and the third switch S3 are inverted, that is, the second switch S2 is turned off and the third switch is turned off. S3 is turned on to reflect the voltage stored in the capacitor (C1) to the input of the N-type source follower to drive.

At this time, when the output voltage discharged from the load of the source follower is smaller than the input voltage, the voltage stored in the capacitor C1 is equal to the difference between the input voltage and the output voltage as the gate voltage of the N-type TFT of the voltage input terminal constituting the N-type source follower. When the output voltage is higher than the input voltage, the gate voltage of the voltage input terminal N-type TFT is further lowered by the voltage stored in the capacitor C1 to drive the output voltage while maintaining the input voltage.

In addition, according to another embodiment of the present invention, as shown in FIG. 9, an analog output buffer circuit may be implemented by connecting a P-type source follower and an N-type follower in a cascode form. In this case, unlike the case where the analog output buffer is implemented by connecting the P-type source and the N-type source follower as described above, each source floor can be connected in cascode form to charge and discharge simultaneously. Initially, the buffer output stage can operate without charging or discharging the load.

In more detail, the analog output buffer circuit shown in FIG. 9 connects a P-type source follower and an N-type source follower to the buffer input terminal in a cascode form, and the buffer output terminal, the P-type source follower and N N-type TFT and P-type TFT are connected between the output terminal of the type source follower, and capacitor C1 is connected between the input terminal of the source follower and the output terminal of the TFT connected to the output terminal of each source follower. It is configured to store the voltage corresponding to.

In addition, an input terminal of the source follower, a buffer output terminal, and a capacitor C1 are turned on to charge or discharge a voltage in the load of the source follower and store a voltage corresponding to the difference between the input voltage and the output voltage in the capacitor C1. The first switch S1 is connected to each other, and is also connected in parallel between the capacitor C1 and the first switch S1, and the contact point between the buffer input terminal and the first switch S1 is connected to the voltage stored in the capacitor C1. Through the second switch (S2) which is turned on to reflect the input of the source follower is connected.

Since the analog output buffer circuit having such a configuration does not need a time for initially charging or discharging the load in the buffer output portion, the analog output buffer circuit is divided into two sections. During the first time, the second switch S2 is turned off. After the first switch S1 is turned on, the input voltage is compared with the voltage charged to the load of the source follower in the previous time, and accordingly, the voltage of the N-type follower is further charged or the P-type source follower is turned on. The input voltage is charged or discharged by discharging the voltage at the load of. That is, if the voltage charged to the load of the source follower in the previous time is larger than the input voltage, the voltage is charged by the N-type source follower, which is the second stage source follower, and conversely, the voltage charged to the load of the source follower in the previous time is If less than the input voltage, the voltage is discharged by the P-type source follower, which is the source follower of the first stage. At this time, the voltage corresponding to the difference between the input voltage and the output voltage is stored in the capacitor C1. Next time, the first switch S1 is turned off and the second switch S2 is turned on to reflect the voltage stored in the capacitor C1 to the input of each source follower.

On the other hand, in the above-described embodiment, each switch is composed of a thin film transistor, that is, a TFT, and may be configured as a P-type TFT switch, an N-type TFT switch, or a transmission gate type switch.

In addition, the embodiments according to the present invention are not limited to the above-described embodiments, and various alternatives, modifications, and changes can be made within the scope apparent to those skilled in the art.

As described above, the present invention implements the analog output buffer used in the source driving circuit of the TFT-LCD panel by using a two-stage source follower and one capacitor using a low temperature poly-Si TFT, thereby increasing the gain in the two-stage configuration. Therefore, as the charging speed is improved, the pixel can be driven within a short time. Also, since the voltage corresponding to the difference between the input voltage and the output voltage is stored in the capacitor and then driven again, the pixel can be driven accurately. It has a driving capability of precision.                     

In addition, since the analog output buffer has a simple structure, the present invention can reduce the area and power consumption, and implement analog circuits under the influence of process variation and kink effect, which require high gradation and high resolution, and have large deviations. Analog output buffers can be applied to tough low-temperature poly-Si TFT-LCD panels, and SOG (System-On-Glass) technology can be developed.

Claims (17)

In the analog output buffer used for the source driving circuit of a TFT-LCD panel, A P-type source follower and an N-type source follower implemented in low temperature poly-Si TFT and connected in series in two stages; A capacitor configured to store a voltage corresponding to a difference between an input voltage and an output voltage of the source follower; A discharge switch which is turned on for a predetermined time to initially discharge the load at the buffer output stage; After the initial discharge is performed, a voltage corresponding to a difference between an input voltage and an output voltage is stored in the capacitor while charging a voltage to the load of the source follower for a predetermined time, or a source follower configured to store the voltage stored in the capacitor at a buffer input terminal. Include multiple switches that are turned on or off to reflect the input of the The P-type source follower and the N-type source follower have a P-type source follower configured at a buffer input stage and an N-type source follower configured at a buffer output stage, and the output of the P-type source follower is connected in series with an input of the N-type source follower. Become, The capacitor is connected in parallel between the voltage input terminal of the P-type source follower and the output terminal of the N-type source follower, The plurality of switches, A first switch connected to an output terminal of the N-type source follower in parallel with the discharge switch and turned off only at the time of initial discharge; A connection between an input terminal of a P-type source follower and the first switch and a capacitor, respectively, which is turned on to charge a voltage of a source follower and store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; 2 switches; A third switch connected in parallel between the capacitor and the second switch, the third switch being turned on to reflect the voltage stored in the capacitor to the input of the P-type source follower through a contact between the buffer input terminal and the second switch; The discharge switch is connected between the first switch and the buffer output terminal in parallel with the ground, and the switching operation opposite to the first switch, analog output buffer circuit for the TFT-LCD panel. delete delete delete delete The method of claim 1, The third switch is turned on during the time of reflecting the voltage stored in the capacitor to the input of the P-type source follower, and if the output voltage charged to the load of the source follower is smaller than the input voltage, the gate of the P-type TFT is equal to the voltage stored in the capacitor. When the voltage is increased and the output voltage charged to the load of the source follower is greater than the input voltage, the gate voltage of the P-type TFT is lowered by the voltage stored in the capacitor so that the output voltage maintains the input voltage. Analog output buffer circuit for source drive of FT-LCD panel. In the analog output buffer used for the source driving circuit of a TFT-LCD panel, An N-type source follower and a P-type source follower implemented in low temperature poly-Si TFT and connected in series in two stages; A capacitor configured to store a voltage corresponding to a difference between an input voltage and an output voltage of the source follower; A charging switch which is turned on for a predetermined time to initially charge a load at the buffer output stage; After the initial charging is performed, a voltage corresponding to a difference between an input voltage and an output voltage is stored in the capacitor at the same time as the voltage is discharged to the load of the source follower, or a source follower configured to store the voltage stored in the capacitor at the buffer input terminal. Include multiple switches that are turned on or off to reflect the input of the The N-type source follower and the P-type source follower have an N-type source follower configured at the buffer input stage and a P-type source follower configured at the buffer output stage, and the output of the N-type source follower is connected in series with the input of the P-type source follower. Become, The capacitor is connected in parallel between the voltage input terminal of the N-type source follower and the output terminal of the P-type source follower, The plurality of switches, A first switch connected to the output terminal of the N-type source follower in parallel with the charging switch and turned off only at the time of initial charging; An input terminal of an N-type source follower and the first switch and a capacitor, respectively, connected to each other to discharge a voltage to a load of the source follower and to store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; 2 switches; A third switch connected in parallel between the capacitor and the second switch, the third switch being turned on to reflect the voltage stored in the capacitor to the input of the N-type source follower through a contact between the buffer input terminal and the second switch, The charging switch is connected in parallel with a predetermined voltage terminal between the first switch and the buffer output terminal, and performs a switching operation opposite to that of the first switch. Circuit. delete delete delete delete The method of claim 7, wherein The third switch is turned on during the time of reflecting the voltage stored in the capacitor to the input of the N-type source follower. When the output voltage charged to the load of the source follower is smaller than the input voltage, the gate of the N-type TFT is equal to the voltage stored in the capacitor. When the voltage is increased and the output voltage charged to the load of the source follower is greater than the input voltage, the gate voltage of the N-type TFT is lowered by the voltage stored in the capacitor so that the output voltage maintains the input voltage. Analog output buffer circuit for source drive of FT-LCD panel. delete In the analog output buffer used for the source driving circuit of a TFT-LCD panel, A P-type source follower and an N-type follower implemented by a low temperature poly-Si TFT and connected in a form of a two-stage cascode; An N-type TFT and a P-type TFT connected in parallel between the buffer output terminal and the output terminal of the P-type source follower and the N-type source follower, respectively; A capacitor connected between an input terminal of the source follower and an output terminal of a TFT connected to an output terminal of each source follower, and configured to store a voltage corresponding to a difference between an input voltage and an output voltage; A first switch turned on to charge or discharge a voltage in the load of the source follower for a predetermined time and to store a voltage corresponding to a difference between an input voltage and an output voltage in the capacitor; A second switch connected in parallel between the capacitor and the first switch, the second switch being turned on to reflect the voltage to the input of the source follower through a contact between the buffer input terminal and the first switch, And the first switch is connected between the buffer input terminal and the input terminal of the source follower, and between the buffer output terminal and the capacitor, respectively. The method of claim 14, The first switch is turned on during the time of charging or discharging the voltage of the source follower, and if the voltage charged to the load of the source follower in the previous time is greater than the input voltage, the load of the N-type source follower, which is the second stage source follower, is greater than the input voltage. The voltage is charged to the load of the P-type source follower, which is the source follower of the first stage, when the voltage charged to the load of the source follower in the previous time is less than the input voltage. An analog output buffer circuit for driving a source of a TFT-LC panel, characterized in that it is held. The method according to claim 1 or 7, And the plurality of switches are any one of a P-type TFT switch, an N-type TFT switch, or a switch of a transmission gate type switch. The method of claim 14, And the first switch and the second switch are any one of a P-type TFT switch, an N-type TFT switch, or a transmission gate type switch.

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