EP1493070A2 - Circuit arrangement for regulating voltage - Google Patents

Abstract

The invention relates to a circuit arrangement for regulating voltage that, in addition to being provided with a control loop having a comparator (4), output stage (3) and a feedback branch, is provided with an auxiliary controller (11 - 14). This auxiliary controller limits the voltage dropping over the output stage (3) and, to this end, comprises a controlling element (11) and another comparator (13). This advantageously enables the output stage (3) of the voltage regulator to have an electric strength lower than the supply voltage that can be supplied to the input (1). The aforementioned voltage regulator is particularly well-suited for supplying on-chip VCO's due to its good suppression of the supply voltage.

Description

description

Circuit arrangement for voltage regulation

The present invention relates to a circuit arrangement for voltage regulation.

Increasingly higher integration densities in integrated circuits usually go hand in hand with a constant decrease in the supply voltage of the integrated circuits. It can happen that semiconductor components with different supply voltages are provided in certain integration technologies. For example, in CMOS (Complementary Metal Oxide Semiconductor) production techniques, transistors for the construction of analog circuits, in particular for the formation of interfaces of the integrated circuit, are provided with a relatively high dielectric strength in addition to transistors which are suitable for the construction of digital circuits and have a significantly lower dielectric strength ha - ben.

In order to supply integrated circuits that require different supply voltages internally with only one external supply voltage, a so-called on-chip voltage regulator is usually provided, which is normally designed as a continuously operating linear regulator. Such voltage regulators should be able to do without external inductors or capacitors.

In particular when controlling resonant circuits, for example for generating high-frequency carrier signals, a voltage regulator is desired to supply the voltage-controlled oscillators usually provided, the output voltage of which has a good supply voltage suppression, English: Power Supply Rejection Ratio, PSRR and at the same time has low self-noise the Not to deteriorate the phase noise of the oscillator to be supplied.

In the document V.R. by KAENEL, A High-Speed, Low-Power Clock Generator for a Microprocessor Application, IEEE Journal of Solid-State Circuits, Vol. 33, No. 11, November 1998, a phase locked loop is specified in a clock generator, which shows a voltage regulator using a circuit diagram in a generalized representation, compare FIG. 2 there.

In the article G.. The best, B. Nauta, Embedded 5 V-to-3.3 V Voltage Regulator for Supplying Digital IC "s in 3.3 Volt CMOS-Technology, IEEE Journal of Solid-State Circuits, Vol. 33, No. 7, July 1998 "A voltage regulator for converting an input voltage of 5 volts into an output voltage of 3.3 volts is indicated in CMOS circuit technology. Figure 2a and 2b show common voltage regulators which as control transistor either use a P-channel MOS transistor, compare Figure 2a , or use an N-channel MOS transistor, see Fig. 2. The gate connection of the control transistor is controlled in each case by a differential amplifier which is provided with a reference voltage, for example by a bandgap circuit, and a derivative from the output voltage of the controller The circuit variant with the PMOS transistor offers a large voltage modulation range, but has the disadvantage of an insufficient supply voltage suppression at frequencies above the amplifier bandwidth. The controller circuit with the NMOS

Although transistor shows good PSRR properties, it has a relatively low achievable output voltage.

If the control transistor in a circuit according to FIG. 2a or 2b of the last-mentioned document is equipped with a dielectric strength that is lower than the input voltage of the voltage regulator, it can, in particular with a mixed oh sh-capacitive load, when the voltage regulator is switched on, a voltage drop above the control transistor is greater than its permissible voltage. If a bandgap voltage source is used for the di ferential amplifier that drives the control transistor, the voltage of which must only build up starting at 0 volts, then the full input voltage is present across the control transistor at the moment of switching on.

The object of the present invention is to provide a circuit arrangement for voltage regulation which is highly integrable and in which a transistor can be used as the control transistor, the dielectric strength of which is lower than the input voltage which supplies the voltage regulator.

According to the invention, the object is achieved by a circuit arrangement for voltage regulation, comprising

an input connection for supplying a supply voltage,

an output connection for tapping an output voltage,

- An output stage comprising a control input and a controlled path with a first and a second load connection, the first load connection being coupled to the input connection of the circuit arrangement and the second load connection being connected to the output connection of the circuit arrangement and via an electrical load to a Reference potential connection is coupled, a reference generator which provides a reference potential at its output,

a comparator which comprises a first input which is connected to the reference generator and which comprises a second input which is coupled to the output terminal of the circuit arrangement for regulating the output voltage, and - An auxiliary regulator for limiting the voltage drop across the output stage, comprising an actuator which is connected on the one hand to the input connection and on the other hand in a circuit node to the controlled path of the output stage, and comprising a further comparator with a setpoint input, which is connected to the control input of the output stage is coupled and with an actual value input which is coupled to the circuit node.

With the auxiliary controller, especially when the voltage controller is switched on, the voltage drop across the output stage is limited to a permissible level. It is thus possible to advantageously implement the output stage with semiconductor components whose dielectric strength is lower than the supply voltage that can be supplied at the input connection.

It corresponds to the present principle that the auxiliary regulator limits the voltage between the circuit node at one of the load connections of the controlled path of the output stage and the control input of the output stage to a maximum voltage amount, for example 0.5 volt. However, as soon as the voltage at the control input of the output stage exceeds a certain value, the actuator forms a closed switch between the input connection and the switching node on the controlled path of the output stage, so that the modulation range of the output stage is not reduced in normal operation.

A so-called floating end is preferably used to control the actuator in the auxiliary regulator by means of the further comparator

Battery provided, which is connected between one of the inputs of the further comparator in the auxiliary controller and the control input of the output stage of the circuit arrangement.

This thus ensures that the potential at the setpoint input of the further comparator in the auxiliary controller is always greater than the potential by a definable voltage amount at the control input of the output stage. As a result, the voltage at the circuit node of the circuit arrangement is set such that it is fundamentally equal to the sum of the voltage at the control input of the output stage and the floating battery voltage. Here, according to the present principle, the restriction applies that the auxiliary regulator automatically limits the voltage at the circuit node to the supply voltage as soon as the voltage at the control input of the output stage exceeds the voltage value that results from the difference in the supply voltage and the fixed voltage amount that the floating voltage Provides battery results. In this case, the auxiliary controller represents a short circuit with regard to its output stage, that is to say a closed switch.

According to a further preferred embodiment of the present invention, the output stage and / or the actuator of the auxiliary regulator are each designed as MOS transistors.

The MOS transistor of the output stage is preferably provided as a MOS transistor designed for low dielectric strength and regular threshold voltage. The MOS transistor of the actuator of the auxiliary regulator is preferably designed as a transistor which is complementary in terms of the conductivity type of the channel to that of the output stage, but has a higher dielectric strength than the transistor of the output stage. The gate connection in each case represents the control input of the actuator or output stage, while the source and drain connection of the MOS transistors each represent the connections of the controlled sections.

A voltage divider is preferably provided to form the signal to be fed back, which is derived from the output voltage and is fed to the comparator which controls the output stage. On the one hand, its interpretation depends on the desired output voltage and on the other hand on the voltage that the reference generator supplies at its output. In bandgap reference sources implemented in silicon technology, this bandgap voltage is usually 1.2 volts.

The comparator of the circuit arrangement, which controls the output stage of the controller, and the further comparator in the auxiliary controller are preferably each designed as differential amplifiers or operational amplifiers, each of which comprises an inverting and a non-inverting input.

The differential amplifier which controls the output stage is advantageously designed such that its output signal can be controlled up to the positive supply voltage.

A further improvement in the suppression of disturbances on the supply voltage can be achieved by developing the circuit arrangement with a further control circuit which supplies the reference generator.

Here, a further control circuit is preferably formed, which comprises an actuator, a comparator and a feedback branch from the actuator to the comparator via a voltage divider. An output of the actuator is coupled to a supply connection of the reference generator. The floating battery, as well as the comparator which controls the output stage and the further comparator which is provided in the auxiliary controller, can also be supplied with advantage by this additional auxiliary voltage.

A switch is preferably provided which can switch the voltage to be supplied to the reference generator for its supply between the actual supply voltage of the control circuit and the auxiliary voltage generated. Further details and preferred embodiments of the present principle are the subject of the dependent claims.

The invention is explained in more detail below using several exemplary embodiments with reference to the drawing. Show it:

FIG. 1 shows a simplified circuit diagram of a first embodiment of the present invention,

FIG. 2 shows an exemplary embodiment for a fixed value voltage source according to FIG. 1 using a circuit diagram,

FIG. 3 shows a further development of the voltage regulator from FIG. 1 with a further control loop,

FIG. 4 shows an exemplary embodiment for the operational amplifiers according to FIGS. 1 and 3 in CMOS circuit technology,

FIG. 5 is a graph showing the voltage profiles of selected node voltages in the circuit of FIG. 1 as a function of the supply voltage,

FIG. 6 shows the switch-on behavior of the circuit from FIG. 1 with interference superimposed on the supply voltage and

FIG. 7 shows an enlarged detail of the diagram from FIG. 6.

FIG. 1 shows a circuit arrangement for voltage regulation with an input connection 1 for supplying a supply voltage of 2.5 volts and an output connection 2 for tapping a regulated output voltage of 1.5 volts. An N-channel MOS field-effect transistor 3 is provided as the output stage, with a gate connection, a source connection and a drain connection. The source connector of output stage 3 forms the output terminal 2 of the circuit. The gate connection is connected to the output of a differential amplifier 4, which works as a comparator and has an inverting and a non-inverting input. The non-inverting input of the comparator 4 is connected to the output of a bandgap reference generator 5, which provides a bandgap voltage of 1.2 volts. The output 2 of the circuit is connected via a voltage divider 6, 7, comprising a series circuit consisting of a 300 ohm resistor 6 and a 1.2 kilohm resistor 7 to the inverting input of the comparator 4 and further coupled to a reference potential connection 8, to which the bandgap generator 5 is also connected. Between the output terminal 2 and the reference potential terminal 8 of the control circuit of FIG. 1, a resistor 9 and, in addition, a capacitor 10 are connected in parallel, which represent a resistive load.

According to the present principle, in order to protect the output stage 3 from the relatively high input voltage or supply voltage when the controller is switched on, a further transistor 11 is provided, which is designed as a P-channel MOS field-effect transistor and with its drain connection in a circuit node 12 of the controller is connected to the drain of output stage 3. The source terminal of the transistor 11 is connected to the input terminal 1 of the regulator circuit. To form the auxiliary controller, a further differential amplifier 13 is also provided, the output of which is connected to the gate terminal of the transistor 11 operating as an actuator. The non-inverting input of the further comparator 13 is connected to the circuit node 12, while the inverting input of the further comparator 13 designed as an operational amplifier is connected to the output of the comparator 4 via a floating battery 14. The connections of the floating battery are provided with the reference numerals 15 and 16. The floating battery raises the potential at the gate of output stage 3 by 0.5 volts and supplies this potential-increased voltage to the inverting input of comparator 13. While the dielectric strength of the NMOS output transistor 3 is only 1.5 volts, the PMOS transistor 11 has a dielectric strength of 2.5 volts.

The control transistor 3 works as a source follower, the source voltage following the gate voltage. The auxiliary regulator, whose actuator 11 is connected into the drain branch of the control transistor 3, causes the drain terminal 12 of the control transistor 3 to be at most 0.5 volts above its gate voltage. This is done by the feedback control of the amplifier 13 and the floating battery voltage of approximately 0.5 volts. The voltage at the circuit node 12 is set by means of the differential amplifier 13 so that it is basically equal to the sum of the voltage at the gate terminal of the transistor 3 and the floating battery voltage of 0.5 volts. In this case, however, it is advantageous that the voltage at the circuit node 12 is automatically limited to 2.5

Volts, namely to the supply voltage, as soon as the voltage at the gate of transistor 3 exceeds 2 volts. In this case, the transistor 11 is a closed switch.

The linear regulator described offers a significantly improved PSSR, Power Supply Rejection Ratio. The additional auxiliary regulator 11, 12, 13, 14 protects the output transistor 3, which only has a dielectric strength of 1.5 volts, from an overvoltage, which otherwise occurs when the regulator is switched on, that is to say during the ramp-up of the control voltage would be immediately between its drain and gate.

According to the principle described, the positive supply voltage of the 1.5 volt fixed NMOS control transistor 3 is held at a value during switching on which is x 0.5 volts above its gate voltage. A breakdown of the control transistor 3 is thus effectively avoided. The relatively thin gate oxide layer and the relatively short channel of the transistor 3 lead to a low strength of its gate-source voltage of only 1.5 volts, but enable the desired, good PSSR, which in particular provides the voltage supply for highly sensitive, voltage-controlled Oscillators are made possible as they are required in resonant circuits, especially in mobile radio.

While transistor 3 is a transistor with a conventional threshold voltage, transistor 11 is designed for analog circuit technology and has a corresponding threshold voltage.

The voltage source 14 can alternatively also be designed as a level shifter or level shifter circuit.

FIG. 2 shows the floating battery 14 from FIG. 1, which provides a voltage at its output connection 15 which is always 0.5 volts higher than the voltage present at its input 16. The output voltage of the voltage source 14 is higher than the input voltage at the node 16 by the amount of the threshold voltage of the PMOS transistor 17. The transistor 17 is connected with its gate connection to the input 16 and connects a reference potential connection 18 with its controlled path with the output terminal 15. The transistor 17 is switched as a source follower and is supplied by a BIAS current source 19, which is connected to the reference potential terminal 18, via a current mirror 20. The current mirror 20 comprises two further PMOS transistors, the gates of which are connected to one another and which are each connected to the supply potential connection 21 of the voltage source 14 by one connection of their controlled paths. The input transistor of the current mirror 20 is connected as a diode. In the present exemplary embodiment, the transistor 17 has a threshold voltage of 0.5 volts. Threshold voltages of PMOS transistors in the range from 0.5 to 0.7 volts are common.

FIG. 3 shows an advantageous development of the voltage regulator arrangement from FIG. 1, which brings about a further improvement in the spread of interference by means of an additional control circuit, which provides an additional, regulated supply voltage for the reference generator 5 and the differential amplifiers 4, 13.

The circuit according to FIG. 3 largely corresponds in structure and advantageous mode of operation to that of FIG. 1 and should not be repeated here to this extent. In the following, only the added components, their interconnection with one another and the additional functionality with their advantages are described.

According to FIG. 3, a further control circuit is provided with an actuator designed as a transistor 22 of the P-channel type with a control input and a controlled path, the control input, that is to say the gate connection of the transistor 22, with a comparator 23 designed as a differential amplifier is connected at the output. The comparator 23 is connected to the input terminal 1 for its voltage supply. The source terminal of the actuator transistor 22 is also connected to the input terminal 1, while the drain terminal forms the output 24 of the further control loop. A regulated voltage of 2.25 volts is provided at this output. Between the output 24 of the further control circuit and reference potential connection 8, a series circuit comprising a resistor 25 of 1.05 kiloohms and a resistor 26 of 1.2 kilohms is connected to form a voltage divider, the tap point for tapping a divided voltage with the inverting Input of the differential amplifier 23 is connected. The non-inverting input of the differential amplifier 23 is connected to the output terminal 15 of the bandgap reference generator 5 for supplying the bandgap voltage at a constant level of 1.2 volts. The output 24 of the further control circuit for supplying voltage to the reference generator 5 is connected to a connection for supplying a supply voltage to the floating battery 14, the differential amplifier 13 and the differential amplifier 4. In addition, a connection to the input terminal 16 of the reference generator 5 is established via a changeover switch 27. Another input of the switch 27 is connected to the input terminal 1 of the circuit for voltage regulation. The changeover switch 27 has a control input for supplying a changeover command, to which a comparator 28 is connected with its output. The comparator 28 has two inputs which are connected on the one hand to the output 24 of the further control circuit and on the other hand to the output 15 of the reference generator 5.

The PMOS regulating transistor 22 provides a regulated voltage with the greatest possible voltage level. The comparator 28 in conjunction with the voltage changeover switch 27 enable the reference generator 5 to be supplied first when the supply voltage is switched on at the connection 1, and later, when the auxiliary voltage tapped at the output 24 has run up, to be switched over to it. As a result, the interference from interference, in particular onto the reference generator 5 and the amplifier 4, can be further reduced, so that the quality of the voltage which can be tapped at the output terminal 2 and is regulated is further improved.

FIG. 4 shows a two-stage operational amplifier constructed using CMOS circuit technology, as is preferably used in the circuits according to FIGS. 1 and 3. In FIG. 1, the operational amplifiers 4 and 13, and in FIG. 3 additionally the operational amplifier 23 are preferably designed as a two-stage operational amplifier as shown in FIG. 4. The operational amplifier according to FIG. 4 has an inverting input 30, a non-inverting input 31 and an output 32. In addition, auxiliary inputs 33, 34 are provided. The operational amplifier is connected between a supply potential connection 35 and a reference potential connection 36. While a changeover command for putting the operational amplifier into an idle state (power down) can be supplied at the auxiliary input 33, a quiescent or bias current, BIAS, can be supplied at the connection 34. The operational amplifier is constructed as a differential amplifier and provides at its output 32 a signal which is dependent on the voltage difference between the signals present at the inputs 30, 31. The operational amplifier 4 is designed in two stages and is equipped with a miller compensation to stabilize the frequency response.

Of particular importance in the operational amplifier according to FIG. 4 when used in a circuit for voltage regulation according to FIGS. 1 or 3 is that the signal which can be tapped at the output 32 can be driven almost up to the positive supply voltage which is supplied at the supply connection 35. This is achieved in the two-stage operational amplifier in that the two complementary output transistors 37, 38 of the output stage of the operational amplifier are both driven with a signal which is dependent on the input differential voltage.

FIG. 5 shows a switch-on process for the voltage regulator from FIG. 1 using a diagram

Voltage levels A, B, C, D plotted as a function of the bandgap voltage provided by the reference generator 5. In the diagram of FIG. 5, this was raised from 0 volt to its nominal value of 1.2 volt for simulation purposes. The fundamentally constant voltage difference of approximately 0.5 volts between level A at the input of the output stage and level B at the circuit node can be clearly seen 12. Only when the supply voltage no longer enables this voltage difference, does the signal level B remain constant, while the level C, which describes the voltage value at the control input of the actuator 11 of the auxiliary regulator, goes to 0 volts. The full supply voltage is thus present at the gate of the transistor. Curve D describes the regulated voltage at output 2 of the circuit. The diagram according to FIG. 5 therefore shows the effective limitation of the voltage drop across the output stage 3.

FIG. 6 shows the course of the supply voltage from 0 volts up to 2.5 volts and back again over the time axis t in the circuit arrangement of FIG. 1. A disturbance with an amplitude of 100 mV is superimposed on the supply voltage. It can be seen that with the regulated output voltage D the value of this disturbance is reduced to 1 mV. The diagram in FIG. 6 thus shows the good PSRR properties, that is to say the good suppression of interference on the supply voltage, which is brought about by the present principle of voltage regulation.

This is particularly clear from the illustration in FIG. 7, which shows an enlarged detail of the diagram in FIG. 6 with a higher resolution of the time axis.

LIST OF REFERENCE NUMBERS

1 input connector

2 output connector 3 output stage

4 comparators

5 reference generator

6 resistance

7 Resistance 9 ohm load

10 capacitive load

11 actuator

12 circuit nodes

13 further comparators 14 fixed value voltage source

15 exit

16 entrance

17 transistor

18 Reference potential connection

Claims

claims 1. Circuit arrangement for voltage regulation, comprising - an input connection (1) for supplying a supply voltage, - an output connection (2) for tapping an output voltage (D), - An output stage (3) comprising a control input and a controlled path with a first and a second load connection, the first load connection being coupled to the input connection (1) of the circuit arrangement and the second load connection being connected to the output connection (2) of the circuit arrangement and is coupled to a reference potential connection (8) via an electrical load (9, 10), a reference generator (5) which provides a reference potential at its output, - A comparator (4) which comprises a first input which is connected to the reference generator (5) and which comprises a second input which is coupled to the output terminal (2) of the circuit arrangement for regulating the output voltage, and - An auxiliary controller (11, 12, 13, 14) for limiting the voltage drop across the output stage, comprising an actuator (11) which couples the input connection (1) with the controlled path of the output stage (3) in a circuit node (12) and comprising a further comparator (13) with a setpoint input which is coupled to the control input of the output stage (3) and with an actual value input which is coupled to the circuit node (12). 2nd Circuit arrangement according to Claim 1, characterized in that a potential-free fixed value voltage source (14) is provided for coupling the setpoint input of the comparator (13) in the auxiliary controller to the control input of the output stage (3). 3. Circuit arrangement according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the floating fixed value voltage source (14) is designed as a floating battery. 4. Circuit arrangement according to one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that the output stage (3) comprises a MOS transistor. 5. Circuit arrangement according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the actuator (11) of the auxiliary controller is designed as a MOS transistor. 6. Circuit arrangement according to one of claims 1 to 5, so that a voltage divider (6, 7) is provided for coupling the output connection (2) of the circuit arrangement to the second input of the comparator (4). 7. Circuit arrangement according to one of claims 1 to 6, that the comparator (4) of the circuit arrangement and the further comparator (13) in the auxiliary controller are each designed as operational amplifiers. 8. Circuit arrangement according to one of claims 1 to 7, characterized in that a further control circuit (22 - 28) is provided for the voltage supply of the reference generator, comprising - an actuator (22) with a control input and a controlled path which the input connection (1) connects the circuit arrangement to an output (24) of the further control circuit and couples it to a supply connection (16) of the reference generator (5), and - A comparator (23) having a first input which is coupled to the output (15) of the reference generator (5), having a second input which is coupled to the output (24) of the further control circuit and having an output which is connected to the Input (16) of the reference generator (5) is connected. 9. Circuit arrangement according to claim 8, characterized in that a changeover switch (27) is provided with a first input which is connected to the input terminal (1) of the circuit arrangement, with a second input which is connected to the output (24) of the further control circuit is connected and with an output which is connected to the input (16) of the reference generator (5). 10. Circuit arrangement according to claim 9, characterized in that a comparator (28) is provided with a first input which is connected to the output (24) of the further control circuit, with a second input which is connected to the output (15) of the reference generator (5) is connected and with an output which is connected to a control input of the switch (27) for supplying a switch command.