KR19990070997A - Signal acquisition circuit of sensing element using current mirror circuit - Google Patents

Abstract

Provided is a signal readout circuit of a high-performance infrared sensing element using a current mirror circuit.

The signal acquisition circuit according to the present invention enables a high integration of the sensing element by requiring only a small area, obtains high injection efficiency due to a small input impedance, and has a small power consumption and a high charge capacity. There is an advantage. In addition, by using the current mirror circuit can stabilize the operating bias voltage (bias voltage) of the infrared sensing element, thereby obtaining a circuit of low noise characteristics.

Description

Signal acquisition circuit of sensing element using current mirror circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel structure of a signal readout circuit for reading electrical signals from a sensing element, and more particularly to a signal acquisition circuit using a current mirror circuit.

In general, the infrared sensing element is implemented by a plurality of identical sensing elements arranged in a one-dimensional or two-dimensional matrix structure, and thus a unit circuit having the same structure also detects a signal acquisition circuit (or a signal acquisition circuit for another type of sensor). It must be implemented by repeating the same number of devices. Such a unit circuit is called an input circuit, a preamplifier, or a unit cell. The most important part of the overall signal acquisition circuit design is the design of such a unit cell. Functions that a unit cell should provide include a function of integrating a signal generated from a sensing device, applying a constant bias to the sensing device, and multiplexing the signals to be sequentially read out.

Conventional circuits known as such unit cells include direct injection circuits (hereinafter referred to as DI circuits), buffered direct injection circuits (hereinafter referred to as BDI circuits), and SFD circuits (Source Follower per Detector circuits). ) And CTIA circuit (Current Transimpedence Amplifier circuit).

As a criterion for evaluating the performance of the unit cell, an injection efficiency indicating how much the signal generated from the sensing element is transmitted to the input circuit and a bias stability indicating how uniformly the bias of the sensing element is held stability, power consumption for operation, and cell area indicating how small an area can be implemented.

In the case of the conventional DI circuit or BDI circuit, it is difficult to maintain the bias voltage of the sensing element at the same voltage uniformly for each element due to the change in the threshold voltage of the entire wafer, resulting in nonuniformity and noise of the circuit. ), And because each unit circuit has to implement an amplifier, a relatively large power consumption is required, and the number of MOSFETs constituting the circuit has limited the device's high integration.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and by using a unit cell circuit using a current mirror circuit in a sensing element signal acquisition circuit, a sensing element having excellent characteristics capable of maintaining almost the same bias voltage of each sensing element. It is to provide a signal acquisition circuit.

It is another object of the present invention to provide a circuit for acquiring a sensing device signal which can be integrated with high power by reducing the number of MOSFETs and has low power consumption.

Still another object of the present invention is to provide a sensing device signal acquisition circuit in which a signal generated from the sensing device can be efficiently transferred to an input circuit due to high injection efficiency.

FIG. 1 illustrates a state in which a unit cell circuit implemented using a current mirror circuit is applied to a signal readout circuit of an infrared sensing element.

2 illustrates a circuit in which the circuit of FIG. 1 is modified to improve noise characteristics.

Figure 3 shows the results of comparing the injection efficiency characteristics of the circuit according to the present invention and the conventional circuit by using a simulation.

Hereinafter, with reference to the accompanying drawings, the configuration and operation of the signal acquisition circuit of the sensing element for achieving the various objects of the present invention described above will be described.

1 is a unit cell circuit of a signal acquisition circuit according to the present invention implemented using a current mirror circuit.

The current mirror circuit according to the present invention consists of two NMOSFETs (M _n1 , M _n2 ) and two PMOSFETs (M _p1 , M _p2 ).

The two PMOSFETs consist of a first PMOSFET (hereinafter referred to as M _p1 ) for passing a reference current and a second PMOSFET (hereinafter referred to as M _p2 ) for flowing the same current as the first PMOSFET current, M _p1 The gates of M _{p2 and} the gates of the gates of the sources are connected to each other to have the same gate-source voltage, and the drain and the gate terminal of M _p2 are connected to each other.

The two NMOSFETs also consist of a first NMOSFET (hereinafter referred to as M _n1 ) for passing a reference current and a second NMOSFET (hereinafter referred to as M _n2 ) for passing the same current as the first NMOSFET current, M _n1 Connect the gate terminal of and M _n2 to each other, connect the cathode (-) of the photovoltage type infrared sensing device to the source of M _n1 , connect the gate and drain of M _n2 , and connect the bias voltage to the sensing device to the source. In the present invention, a voltage such as 0 V) is applied.

In addition, the same current flows, and the sensing device is connected to the drain and the drain of M _p2 of the connected M _n1, either directly or indirectly, to a source terminal connected to the drain terminal and the drain terminal of M _p1 of M _n2 through the M _n2 and M _p1 Through M _n1 and M _p2 , the same amount of current, that is, the photocurrent induced in the sensing element, flows.

Further, in addition to the above-described configuration the integration between a direct connection to the drain of the drain and M _p2 of M _n1 and two PMOSFET M _p1 and connected to a capacitor for integration to the source terminal of the M _p2, or, M _n1 and the drain of M _p2 A capacitor may be connected and a supply voltage (VDD) may be applied to the source terminals of the two PMOSFETs M _p1 and M _p2 .

The principle of operation of the circuit is that when the photocurrent I _ph generated from the photo-voltaic infrared sensing circuit flows through the MOSFET transistors M _n1 and M _p2 , M _p1 and M _p2 of the same dimensions are current mirrors. M _p1 to flows a current (I _ph) of the current and the size of passing through the M _p2, is caused to flow, the current all of the four transistors being current flows (I _ph), such as in M _n2. (Note that M _p1 And M _p2 are perfectly matched so that the gate-source voltage (V _GS ) is the same, and the same drain current flows. In addition, if M _n1 and M _n2 are perfectly matched, since the same current (I _ph ) has the same magnitude of gate-source voltage (V _GS ), the source voltage of M _n1 is equal to the source voltage of M _n2 . It will keep the same 0V. The source voltage of M _n1 , which is maintained at 0 V, becomes the bias voltage applied to the sensing element, and the bias voltage of the sensing element will be maintained at 0 V regardless of the current flowing through the sensing element.

FIG. 2 is a circuit for improving noise characteristics. In the circuit of FIG. 1, a signal accumulated in an integrating capacitor, which collects an optical signal, doubles the photocurrent I _{ph because the} current through M _p1 and the current through M _p2 are combined. In this case, a difference in current may occur due to a difference in threshold voltage between M _p1 and M _p2 , and as a result, noise may be generated in the integrated optical signal. The circuit has been modified. Here, the threshold voltage mismatch does not affect the uniformity. However, although the threshold voltage mismatch may affect the sensing element bias voltage, the effect is very small.

In the conventional DI circuit or BDI circuit, it is difficult to maintain the bias voltage of each sensing element at the same value by changing the threshold voltage of the entire wafer. However, in the circuit of the present invention, the bias voltage of the sensing element is increased. By only relating the threshold voltage mismatch between M _n1 and M _n2 and M _p1 and M _p2 , the variation of the bias voltage can be maintained at a very narrow level. In addition, even when the amount of current flowing through the MOSFET changes due to the change in the photocurrent, the source voltage of M _n2 , that is, the bias voltage of the sensing element does not change, but the gate voltage of M _n2 changes, so the input impedance of the input circuit is very small. As a result, a high injection efficiency is obtained. This improvement in implantation efficiency will be described below with reference to FIG. 3.

Since the power consumption required to drive the circuit only needs to flow twice as much photocurrent, each unit circuit generally requires less power than the BDI circuit, which requires an amplifier. As a result, since a small area can be implemented, a signal acquisition circuit of a high density infrared sensing element can be provided.

Figure 3 shows the result of comparing the injection efficiency characteristics of the circuit according to the present invention and the conventional circuit, I _D means the light current flowing through the infrared sensing element, R _D A is the area and resistance of the sensing element Multiplied by In addition, DI means a direct injection circuit, BDI means a buffer direct injection circuit, and a gain value means an amplification factor of a feedback amplifier used in the BDI circuit. In general, the injection efficiency is higher as the light current is larger, the larger the R _D A, the circuit according to the present invention shows an injection efficiency close to 100% at almost all the R _D A value is superior to the conventional circuit It can be seen that it shows characteristics.

Claims (3)

A signal acquisition circuit of a sensing element using a current mirror circuit, The current mirror circuit is composed of two NMOSFETs (M _n1 , M _n2 ) and two PMOSFETs (M _p1 , M _p2 ), The two PMOSFETs are composed of a first PMOSFET (hereinafter referred to as M _p1 ) for passing a reference current and a second PMOSFET (hereinafter referred to as M _p2 ) for flowing the same current as the first PMOSFET current, and M The gates of _p1 and M _p2 are connected with the gates and the sources with the sources, and the drain and the gate terminals of M _p2 are connected with each other, The two NMOSFETs also comprise a first NMOSFET (hereinafter referred to as M _n1 ) for passing a reference current and a second NMOSFET (hereinafter referred to as M _n2 ) for flowing the same current as the first NMOSFET current, M connecting the gate terminal of _n1 and M _n2 each other, and a source of M _n1, the negative electrode of the photoelectric pressure type sensing element (-) connected to, and connecting the gate and drain of M _n2 and as a bias voltage line source, walking in the sensing element Apply voltage, Connecting the drain terminal of M _n2 drain terminal and M _p1 of, and the amount of current, such as to connect the drain terminal and the drain terminal of M _p2 of M _n1, either directly or indirectly, through the two MOSFET M _n1, M _p2, that is detected A signal acquisition circuit of a sensing element, characterized in that for flowing the photocurrent (I _ph ) induced in the element. 2. The signal acquisition circuit of claim 1, wherein a drain of M _n1 and a drain of M _p2 are directly connected, and a capacitor for integration is connected between the source terminals of the two PMOSFETs. The method of claim 1, wherein a capacitor for integration is connected between the drain of M _{n1 and} the drain of M _p2 , and a power supply voltage VDD is connected to source terminals of the two PMOSFETs. Circuit.