RU2544780C1 - Low-voltage cmos current mirror - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to radio engineering and electronics, particularly to analogue microcircuits for different purposes, and can be used as a functional unit in operational amplifiers, comparators and other units. To this end, the invention discloses a current mirror comprising circuitry-identical input and output stages, each including two MOS transistors connected in series between a first power supply bus and an input or output, respectively, as well as an active control circuit which includes a resistor and an additional MOS transistor, connected in series between the series connection point of input (output) transistors and a second power supply bus. The gates of the additional transistors are connected to the input and output of the current mirror.

EFFECT: high output resistance of the current mirror and the corresponding accuracy of current transmission.

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Description

The invention relates to the field of radio engineering and electronics, in particular to analog integrated circuits and blocks based on CMOS transistors with nanometer-sized elements.

The development of CMOS technology is on the way to reducing the size of elements. In this case, the supply voltage of the chips and the output resistance of the transistors inevitably decrease. The static parameters of analog blocks depend on the supply voltage and the output resistance of the transistors. The new circuitry solution is aimed at increasing the output resistance of current sources with a minimal increase in the complexity of the circuit and the corresponding area on the chip.

In well-known technical solutions, the stabilization of the output current is achieved by sequential (cascode) switching on the MOS transistors in the input and output circuits, as well as by introducing an additional regulator controlling one of the output transistors into the circuit [1, 2, 3, 4]. Simple cascode inclusion of the same MOS transistors reduces the range of voltage changes at the output of the current mirror.

The introduction of an additional controller based on an operational amplifier significantly complicates the circuit and increases the block area on the chip chip and power consumption [4].

The closest technical solution is the current mirror described in the literature [5]. The prototype contains identical input and output stages with series-connected MOS transistors having different threshold voltages and active control circuits in the input and output stages.

The simplest technical solution to increase the output resistance of a current mirror is the series connection of two MOS transistors in the output circuit. An additional increase in output resistance is achieved by choosing the threshold voltage of the MOS transistors of the input and output circuits. The threshold voltage of a transistor connected by a drain to the output of a current mirror should be less than that of a transistor connected by a source to a power bus.

Technologically, the easiest way to reduce the threshold voltage of MOS transistors is to not additionally dope the substrate at the transistor locations. This results in a natural transistor with a threshold voltage close to zero.

A simple technical solution does not provide an increase in output resistance tens or hundreds of times. A multiple increase in output resistance is achieved by introducing into the circuit an active control circuit based on an operational amplifier, which increases power consumption and unit area.

According to the invention, the technical result is achieved by simplifying the active control circuit, including a source follower based on a MOS transistor with a depletion of the channel and a resistor connecting the source of this transistor to the drain of the MOS transistor, the source of which is connected to the first power bus. Increasing the output voltage of the current mirror increases the current in the output circuit. Compensation for changes in the output current is achieved when the value of the output resistance of the current mirror is equal without the control circuit and the resistance of the resistor in the control circuit. An additional reduction in the area of the current source is achieved by replacing the resistor in the control circuit with a MOS transistor in the resistor mode with a gate connected to the power bus. MOS transistors with enrichment and depletion of the channel can be implemented in the chip simultaneously by selective doping of the substrate. Serial (cascode) switching of MOS transistors increases the output resistance of the current mirror, however, a decrease in the supply voltage of the microcircuit does not allow full compensation of the dependence of the output current on the output voltage without active regulation.

The objective of the present invention is to increase the output impedance of the current mirror and increase the accuracy of current transfer without increasing power consumption and circuit complexity.

The low-voltage CMOS current mirror is built on the basis of the input and output stages. Each of the stages includes two MOS transistors of the first type of conductivity, connected in series between the first power bus and the input / output of the current mirror, respectively. Moreover, the transistors connected by the source to the first power bus have a higher threshold voltage, and the transistors connected by the drain to the input / output have a threshold voltage of the opposite sign. The gates of all transistors are connected to the input of the current mirror, and the contacts to the substrate are connected to the first power bus.

A distinctive feature of the invention is a simplified circuit of active control circuits, including a MOS transistor of the first type of conductivity with a threshold voltage of the opposite sign and a limiting resistor. Moreover, the drain of the transistor is connected to the second power bus, the contact to the substrate to the first power bus, and the resistor is connected between the source of the MOS transistor and the serial connection point of the input / output transistors. The gate of the MOS transistor is connected to the input / output of the current mirror

In the active control circuit, the depth of negative feedback is determined by the resistance of the resistor. The source follower in the active control circuit diverts a portion of the output current to the power circuit. The magnitude of the output current is determined by the resistance of the resistor in the active control circuit. Choosing the nominal value of the resistance in the control circuit, you can control the output resistance of the current mirror. Moreover, it is possible to realize a negative value of the output resistance of the current mirror.

An alternative is possible, which allows not to use high-resistance resistors in the circuit that require additional technological operations. For this, in the active control circuit, the resistor is replaced by a MOS transistor of the second type of conductivity with a gate connected to the first power bus and a contact to the substrate connected to the second power bus.

A distinctive feature of the invention is the use of a source follower with channel depletion in the active control circuit, which ensures equal voltages at the output transistor and at the resistor in the control circuit and, as a result, the linear nature of the current increase in the control circuit with increasing output voltage.

Figure 1 and 2 shows a diagram of a low-voltage current mirror based on MOS transistors with depletion and enrichment of a channel having active control circuits, where:

1 - input stage;

2 - output stage;

3 - the first power bus;

4 - input current mirror;

5 - current mirror output;

6 - input transistor with a high threshold voltage;

7 - input transistor with a reduced threshold voltage;

8 - resistor (MOS transistor) input circuit active regulation;

9 - MOS transistor with a depletion of the channel in the input circuit of the active regulation;

10 - output transistor with a high threshold voltage;

11 - output transistor with a reduced threshold voltage;

12 - resistor (MOS transistor) output circuit active regulation;

13 - MOS transistor with a depletion of the channel in the output circuit of the active regulation;

14 - second power bus.

Figure 2 shows a diagram of a low-voltage current mirror with improved thermal stability of parameters due to the use of MOS transistors instead of resistors, pos. 8 and pos. 12.

The resistor in the active control circuit can be made both in the form of a doped polysilicon conductor and in the form of a MOS transistor with channel enrichment. In this case, its shutter is connected to the second power bus, and the contact to the substrate to the first power bus. Replacing the resistor with a MOS transistor reduces the temperature dependence of the output resistance of the current mirror.

A low-voltage current mirror based on MOS transistors with channel enrichment and depletion, including active control circuits, provides an increase in the output resistance and current transmission accuracy with a minimum increase in the complexity and area of the block on the chip chip.

A distinctive feature of the technical solution is the integrated use of cascode switching of MOS transistors with enrichment and depletion of the channel together with the simplest active control circuit.

A current mirror with a high output resistance includes circuit-identical identical input and output stages; each based on two MOS transistors of the first type of conductivity, connected in series between the first power bus and the input (output) of the current mirror, respectively.

Transistors connected by a source to the first power bus have a structure with channel enrichment and increased threshold voltage, transistors connected by a drain with input (output) have a channel depletion structure and threshold voltage of opposite sign; the gates of the transistors are connected to the input of the current mirror, and the contacts to the substrate are connected to the first power bus. Active control circuits based on a series-connected resistor and a MOS transistor with channel depletion and first-type conductivity are introduced into the input and output stages, and the drains of these transistors are connected to the second power bus, the contacts to the substrate to the first power bus, and the gates to the input or current mirror output, respectively; the sources through the resistors are connected to the serial connection points of the input (output) transistors, respectively; the contacts to the substrate of all transistors are connected to the first power bus.

Figure 3 shows the result of calculating the change in the output resistance of the current mirror when an active control circuit is connected.

The selection of the resistor value or the width of the MOS transistor of the second type of conductivity in the active control circuit allows you to increase the value of the output resistance of the current mirror and even get its negative value.

The proposed technical solution allows simple means to control the output impedance of the current source and to obtain a large gain in one amplifier stage due to the negative differential resistance of the load current source.

Information sources

1. US patent No. 4550284.

2. RF patent No. 2365969.

3. RF patent No. 2362202.

4. S. Yan, E. Sanches-Sinencio, Low voltage analog circuit design techniques., IEICE Transactions on Analog integrated circuits and systems, vol. E00-A, No.2, p. 1-17, 2000.

5. T. Serrano, Linares-Barranco, The active-input regulated-cascode current mirror, IEEE Transactions on Circuits and Systems 11: Analog and Digital Signal Processing, vol. 41, p. 464-467, June 1994 (prototype).

Claims (1)

The low-voltage CMOS current mirror, including the input and output stages, each based on two MOS transistors of the first type of conductivity, connected in series between the first power bus and the input / output of the current mirror, respectively, and the transistors connected by the source to the first power bus have an increased threshold voltage and the transistors connected by the drain to the input / output have a reduced threshold voltage or threshold voltage of the opposite sign, the gates of all transistors are connected to the current input of the second mirror, and the contacts to the substrate with the first power bus, characterized in that active control circuits are introduced based on the series-connected resistor and MOS transistor with the first type of conductivity and a reduced threshold voltage, and the drains of these transistors are connected to the second power bus, the contacts are to the substrate, that is, to the first power bus, and the gates to the input or output of the current mirror, respectively, and the sources through resistors are connected to the serial connection points of the input or output transistors accordingly, the contacts to the substrate of the transistors in the active control circuits are connected to the first power bus, or series-connected MOS transistors of the first type of conductivity with a low threshold voltage and MOS transistors with a high threshold voltage, and the gate of the transistor with a high threshold voltage is connected to the second power bus, and the contact to the substrate is with the source.

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