JP2001251170A - Oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To insure sufficient oscillation frequencies in the low voltage region of a ring oscillation circuit, to also suppress the rise of the oscillation frequency in a high voltage region and to reduce current consumption in a MOS semiconductor integrated circuit device. SOLUTION: This device has a first constant voltage generation circuit 2a consisting of a P type MOS enhancement transistor 21 and an N type MOS depression transistor 22 and a second constant voltage generation circuit 2b consisting of an N type MOS depression transistor 23 and an N type MOS enhancement transistor 24. A first constant voltage generated by the first constant voltage generation circuit is applied to the gate electrode of the P type MOS transistor of a transmission gate 26 connected between inverter circuits constituting a ring oscillation circuit, and a second constant voltage generated by the second constant voltage generation circuit is applied to the gate electrode of the N type MOS transistor of the gate 26. Electronic equipment composed of an EEPROM that is small-sized and has a long life can be realized by using such a ring oscillation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MOS integrated circuit, and more particularly to a ring oscillation circuit which operates with a small difference in oscillation frequency over a wide power supply voltage range. The present invention also provides
Electrically rewritable nonvolatile semiconductor memory integrated circuit (E
In particular, EPROM ICs that can operate with a single power supply that operate with low power consumption in a wide range from a low voltage to a wide power supply voltage.
It relates to an EPROM IC.

Further, the present invention relates to an EEPROM for storing information by receiving energy from a battery such as a solar battery.
The present invention relates to an electronic storage device including an IC, and particularly to a small and long-life electronic storage device.

[0003]

2. Description of the Related Art Conventionally, in a semiconductor integrated circuit, a ring oscillation circuit in which an odd number of inverter elements and the like are simply connected in a ring shape has been used as the simplest oscillation circuit.
In addition, there is a single power supply EEPROM IC that generates a voltage several times higher than the power supply voltage by driving a booster circuit with a ring oscillator and can perform program erasure. For example,
It is described in JP-A-5-325578.

[0004]

However, since the oscillation frequency of the conventional ring oscillation circuit greatly fluctuates with respect to the fluctuation of the power supply voltage, when operating with a wide power supply voltage, a sufficient oscillation frequency in a low voltage region is obtained. If it is attempted to secure the oscillation frequency, the oscillation frequency in the high voltage region becomes unnecessarily high, so that there is a problem that current consumption increases.

[0005] In an EEPROM operated by a single power supply,
Inside, a voltage higher than the power supply voltage is generated using a booster circuit by driving a ring oscillator. However, when the booster circuit is designed to operate from a power supply voltage as low as about 1 V, power consumption increases significantly when the power supply voltage is high.

[0006] Therefore, in an electronic device of the EEPROM IC programmed by a solar cell or the like, a large-sized solar cell is required. In addition, in an electronic device using a dry battery, there is a problem that the life of the battery is short. An object of the present invention is to obtain a stable oscillation frequency by controlling a power supply voltage of an oscillation circuit or limiting a current.

Another object of the present invention is to provide an EEPROM IC in which the power consumption does not increase significantly with an increase in the power supply voltage in the operation from a low voltage to a wide power supply voltage. It is a further object of the present invention to provide an electronic storage device that can be programmed using a small solar cell.

[0008]

In order to solve the above problems, the present invention provides a constant voltage generating circuit,
Either the ring oscillation circuit itself is operated at a constant voltage, or a ring oscillation circuit is provided which includes a constant voltage generation circuit and a constant current element controlled by the constant voltage generated by the constant voltage generation circuit.

In a nonvolatile memory device, a memory cell array having memory means, a ring oscillation circuit, and a power supply voltage boosted by driving the ring oscillation circuit to increase a power supply voltage higher than a power supply voltage necessary for writing and erasing of the memory means. A booster circuit that generates a voltage pulse, wherein the ring oscillation circuit is connected to a plurality of odd-numbered inverting circuits in a ring, a constant current circuit is connected to each of the inverting circuits, and a constant current value of the constant current circuit. The rising characteristic of the high voltage pulse is controlled based on the gate capacitance of the inverting circuit. Further, in a non-volatile memory device, a memory cell array having memory means, a ring oscillation circuit having an odd number of inverting circuits connected in a ring, and a power supply voltage boosted by driving the ring oscillation circuit to write the memory means; A booster circuit for generating a high-voltage pulse for programming higher than a power supply voltage required for erasing, and wherein the ring oscillation circuit is driven at a constant voltage by a constant voltage generation circuit.

[0010]

By using the ring oscillation circuit configured as described above, it is possible to secure a sufficient oscillation frequency in a low voltage region and to reduce current consumption without largely changing the oscillation frequency in a high voltage region. Becomes possible.

In a memory card composed of a plurality of EEPROM ICs, the current consumption at the time of programming can be reduced to half or less of that of the conventional one, so that a memory card operated by a solar cell can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the ring oscillation circuit of the present invention. The power supply of the ring oscillation circuit 1 is connected to the constant voltage generation circuit 2, and the output of the ring oscillation circuit 1 is connected to the level conversion circuit 3.

FIG. 2 is a circuit diagram of a first embodiment of the ring oscillation circuit of the present invention. In FIG.
Depletion transistors 11 and 12 and N-type MO
The ring oscillation circuit 1 constituted by the five inverters 10 oscillates under a constant voltage generated by the constant voltage generation circuit 2 constituted by the S enhancement transistor 13.

The output signal of ring oscillation circuit 1 is supplied to waveform shaping inverters 14 and 1 which also operate at a constant voltage.
After waveform shaping at 5, the signal enters the level conversion circuit 3 composed of P-type MOS enhancement transistors 16 and 17 and N-type MOS enhancement transistors 18 and 19, and finally becomes a signal having the same amplitude as the power supply voltage.

Since the ring oscillation circuit in FIG. 2 always operates at a constant voltage, the oscillation frequency is constant regardless of the power supply voltage. FIG. 3 is a block diagram showing a second embodiment of the ring oscillation circuit of the present invention. The constant current element 4 is connected between the inverters 5 and the constant current element 4 is connected to the constant voltage generation circuit 2.
Connected to.

FIG. 4 is a specific circuit diagram of a second embodiment of the ring oscillation circuit of the present invention. In FIG.
A first constant voltage is generated by a first constant voltage generating circuit 2a composed of an OS enhancement transistor 21 and an N-type MOS depletion transistor 22, and an N-type MOS depletion transistor 23 and an N-type MOS
A second constant voltage is generated by a second constant voltage generation circuit 2b constituted by the S enhancement transistor 24.

Each inverter 2 constituting the ring oscillation circuit
5, a transmission gate 26 is inserted, and the P-type M of the transmission gate is inserted.
A first constant voltage is applied to the gate electrode of the OS transistor, and a second constant voltage is applied to the gate electrode of the N-type MOS transistor. Therefore, the transmission gate 26 functions as a kind of constant current element.

In FIG. 4, the charge Q charged and discharged to the gate electrode capacitance of the inverter element 25 constituting the ring oscillation circuit is expressed by the following equation. Q = Cg · E (Equation 1) Q = Itg · dt (Equation 2) = Itg · t (Equation 2 ′) Q: Electric charge accumulated in the gate electrode of the inverter Cg: Gate electrode capacitance of the inverter E: Power supply voltage Itg: Current flowing through the transmission gate t: Charge / discharge time Equation 2 represents the case where Itg is a function of the charge / discharge time t, and the constant voltage generation circuit 2 operates stably in the oscillation circuit of FIG. 4 according to the present invention. In consideration of a power supply voltage region sufficient for (1), Itg is considered to be constant irrespective of time, and therefore, Expression 2 is expressed by Expression 2 '.

Therefore, the charging / discharging time t is expressed by the following equation 3 from the equations 1 and 2 '. t = (Cg / Itg) · E (Equation 3) In Equation 3, Cg and Itg are considered to be constants, so that the charging / discharging time t is proportional to the power supply voltage E.
The oscillating frequency is inversely proportional to the power supply voltage E, as expressed by the equation (4), contrary to the ordinary simple ring oscillating circuit.

F = 1 / 2t = (1/2) · (Itg / Cg) · (1 / E) (Equation 4) FIG. 5 is a block diagram showing a third embodiment of the ring oscillation circuit of the present invention. It is. Each of the constant current elements 4 is connected to the inverter 5, and each of the constant current elements 4 is connected to the constant voltage circuit 2.
It is connected to the.

FIG. 6 is a specific circuit diagram of a third embodiment of the ring oscillation circuit of the present invention. In FIG.
A first constant voltage is generated by a first constant voltage generation circuit 2a composed of an OS enhancement transistor 31 and an N-type MOS depletion transistor 32, and an N-type MOS depletion transistor 33 and an N-type MO
The second constant voltage is generated by the second constant voltage generating circuit 2b constituted by the S enhancement transistor 34 in the same manner as in the embodiment of FIG.

In the inverter constituting the ring oscillation circuit in the embodiment shown in FIG. 6, P-type MOS enhancement transistors 35 and 36 and N-type MOS enhancement transistors 37 and 38 are all connected in series. A first constant voltage is applied to the gate electrode of the P-type MOS enhancement transistor 35, and the P-type MOS
The gate electrode of the enhancement transistor 36 is connected to the output of the preceding inverter.

Further, a second constant voltage is applied to the gate electrode of the N-type MOS enhancement transistor 38, and the output of the preceding inverter is connected to the gate electrode of the N-type MOS enhancement transistor 37. A P-type MOS enhancement transistor 35 to which a first constant voltage is applied and an N-type MOS enhancement transistor 38 to which a second constant voltage is applied
Works as a kind of constant current element like the transmission gate in the embodiment of FIG.

Accordingly, the oscillation frequency of the ring oscillation circuit shown in the embodiment of FIG. 6 is inversely proportional to the power supply voltage, similarly to the circuit of the embodiment of FIG. FIG. 7 is a block diagram showing a configuration of an EEPROM IC using the oscillation circuit of the present invention. As a memory means, a bit line control circuit 72 for writing and reading data to and from the memory cell array 71 is provided.

The bit line control circuit 72 is connected to a data input / output buffer 76, and receives an output of a column decoder 73 which receives an address signal from an address buffer 74 as an input. Further, a row decoder 75 is provided for the memory cell array 71 to control a control gate and a selection gate. A memory IC is provided by a circuit or the like that controls each function of the memory cell array 71.
Is configured.

The booster circuit 78 receives a drive signal from a ring oscillator 79 as an oscillation circuit and applies a voltage boosted from a power supply voltage to the memory cell array 71 when writing / erasing (called a program including both operations). It is supplied to the bit line control circuit 72 and the row decoder 75.

FIG. 8 is a sectional view of the EEPROM memory cell. A floating gate transistor 82 and a select gate transistor 83 are electrically connected in series to a P-type silicon substrate 81. The floating gate transistor 82 has a floating gate electrode 87 on a channel region between an N-type source region 84 and a drain region 85 via a gate insulating film 86.
And a control gate insulating film 88 and a control gate electrode 89. The drain region 85 and the floating gate electrode 87 are formed so as to overlap with each other via a tunnel insulating film 801 having a thickness of about 70 to 100 °.

By applying a high voltage between the control gate electrode 89 and the drain region 85, a tunnel current flows through the tunnel insulating film and the amount of electrons to the floating gate electrode 87 can be changed for programming. The non-volatile data is programmed by changing the channel conductance of the floating gate transistor according to the amount of electrons of the floating gate electrode 87.

Generally, when a high electric field is suddenly applied to the tunnel insulating film 801, dielectric breakdown easily occurs. Therefore, as a high voltage at the time of programming to the control gate electrode or the drain region, a rising pulse of several tens μsec to several hundred μsec is applied. In the oscillation circuit of the present invention, since the current flowing through each of the inverting circuits constituting the ring oscillator is controlled, by reducing the current value, a special charging capacitor for controlling the rise time can be provided. No longer needed. That is, as in the circuits of the embodiments of FIGS. 4 and 6, only the capacitance of the gate electrode itself of the transistor constituting the inverting circuit can function as a charging capacitor. Therefore, a special capacitor or circuit for controlling the ramping of the program pulse becomes unnecessary, and the size of the IC can be reduced.

As described above, the oscillation circuit of the present invention is
An EEPROM that operates with a single power supply with a wide range of power supply voltage of about 0.7 V to 6 V by applying to a PROM IC
An IC can be realized with a simple circuit. Further, the power during operation can be reduced to less than half of the conventional power.

In the case of an EEPROM IC, the power consumption is most often at the time of programming using a high voltage internally. Therefore,
The EEPROM IC of the present invention can reduce the current consumption during programming to about half or less without deteriorating the programming characteristics. The above-described EEPROM IC is suitable for a battery-operated memory device. Suitable for very small required battery operated electronic devices. For example, when a mobile communication device uses a solar cell as its energy source, the EEPROM IC of the present invention is suitable.

[0032]

As described above, in the present invention, a ring oscillator is provided with a constant voltage generating circuit or a constant voltage generating circuit and a constant current element controlled by a constant voltage generated by the constant voltage generating circuit. Is effective in securing a sufficient oscillation frequency even when the power supply voltage is in a low voltage region, suppressing an increase in the oscillation frequency in a high voltage region, and reducing current consumption.

The present invention also provides an EEP operating at less than half the power consumption of a conventional device at a wide range of power supply voltage of about 0.7 V to 6 V.
A ROM IC can be realized. Further, it is possible to realize a very small electronic device including an EEPROM IC operated by a battery having a long life.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a ring oscillation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a ring oscillation circuit according to the present invention.

FIG. 3 is a block diagram showing a second embodiment of the ring oscillation circuit according to the present invention.

FIG. 4 is a circuit diagram showing a second embodiment of the ring oscillation circuit according to the present invention.

FIG. 5 is a block diagram showing a third embodiment of the ring oscillation circuit according to the present invention.

FIG. 6 is a circuit diagram showing a third embodiment of the ring oscillation circuit according to the present invention.

FIG. 7 shows an EEPROM using an oscillation circuit according to the present invention.
It is a block diagram of IC.

FIG. 8 is a sectional view of an EEPROM memory cell according to the present invention.

[Explanation of symbols]

1, 79 ring oscillation circuit 2 constant voltage generation circuit 4 constant current element 5, 10, 14, 15, 20, 25, 27, 39 inverter circuit 11, 12, 22, 23, 32, 33 N-type MOS depletion transistor 13, 18, 19, 24, 34, 37, 38 N-type MO
S enhancement transistor 16, 17, 21, 31, 35, 36 P-type MOS enhancement transistor 26 transmission gate 71 memory cell array 78 booster circuit

Claims (1)

[Claims] 1. A P-type MOS transistor connected in series between power supplies.
Invar consisting of transistor and N-type MOS transistor
Ring oscillator circuit with an odd number of stages connected in cascade,
The P-type MOS transistors of the respective inverter circuits;
P type connected between the source of the star and one power supply voltage
A plurality of first constant current elements composed of MOS transistors
And the N-type MOS transistors of the respective inverter circuits.
Connected between the source of the transistor and the other supply voltage
A plurality of second constant currents each comprising a P-type MOS transistor
Device, P-type MO with gate and drain connected in common
S enhancement transistor, gate and source
N-type MOS depletion transistors connected in common
The first constant voltage generation circuit in which the
, The gate and the drain of which are connected in common.
MOS enhancement transistor, gate and SO
N-type MOS depletion transformer with common source
A second constant voltage in which a transistor is connected in series between the power supply voltages
Generating circuit, and the P-type MOS enhancement of the first constant voltage generating circuit
And the N-type MOS depletion transistor
The connection point of the transistor constitutes the first constant current element.
Connected to the gate of the P-type MOS transistor
The N-type MOS enhancement method of the second constant voltage generation circuit.
Transistor and the N-type MOS depletion transistor
The connection point of the transistor constitutes the second constant current element.
The gate of the N-type MOS transistor is connected
An oscillation circuit characterized by the above .