JPH0389610A - Differential amplifier with auto-zero unction and sample and holde function - Google Patents

Abstract

PURPOSE:To obtain a differential amplifier with the auto-zero function and the sample and hold function quicker than conventional are by starting the auto-zero operation of the differential amplifier in the hole state of a sample and virtually shortening the time of the auto-zero operation. CONSTITUTION:The offset voltage of a differential amplifier 100 is held in offset voltage holding capacities 10A and 10B by the auto-zero operation. A switch 4 is opened, and a switch 3 is closed, and switches 8A and 8B are closed, and switches 12A and 12B are opened, and then, the voltage obtained by amplifying the difference between an input signal 1 and a reference signal 2 appears in output terminals of sample and hold circuits 200A and 200B. When switches 8A and 8B are opened next, the voltage of differential voltage holding capacities 11A and 11B and the voltage in output terminals of sample and hold circuits 200A and 200B are kept constant though the input signal 1 and the reference signal 2 are changed. The switch 3 is opened and the switch 4 is closed at this time, and thereby, the differential amplifier 100 already enters into the auto-zero operation when sample and hold circuits 200A and 200B perform the holding operation.

Description

[Detailed description of the invention] Industrial application field The present invention is an auto-zero machine that amplifies the difference between two signals.
Regarding differential amplifiers with sample and hold functions, prior art FIG. 1 shows the configuration of a conventional auto-zero differential amplifier with sample and hold functions, and FIG. 4 shows its timing.

In the differential amplifier 100 of FIG. 1, it is ideal that the characteristics of the MOS transistors 5A, 5 and the resistors 6A, 6BJ are equal to each other. Even if the output voltage of this differential amplifier (in addition to the voltage that amplifies the difference between input signal 1 and reference signal 2) always includes a constant voltage, that is, an offset voltage, in order to perform accurate differential amplification ( This offset voltage must be removed~1 The auto-zero mechanism shown in Figure 1 Amplification of the difference between input signal 1 and reference signal 2 in the differential amplifier with sample and hold function is performed as follows.

Step 1 (Auto zero) Close switch 4 and open switch 3.

At that time, even if an offset voltage appears at the output terminal of the differential amplifier 100, by further closing the switches 8A, 8B, and 12A, 12B, the offset voltage holding capacitor 10A is connected to the IOB (upper differential amplifier 100).
Even if the offset voltage of is held, Step 2 (sample) Next, if switch 4 is opened and switch 3 is closed,
At the output terminal of the differential amplifier 100, a voltage obtained by adding an offset voltage to the voltage obtained by amplifying the difference between input signal 1 and reference signal 2 appears. A voltage that amplifies the difference between the input signal 1 and the reference signal 2 appears at the output terminals of the sample and hold circuits 200A and 200B.
The voltage appearing at the output terminals of the sample and hold circuits 20OA and 200B does not include the offset voltage of the differential amplifier 100 (1 Step 3 (Hold)) Then switch 8A and 8B.Then, the voltages of the differential voltage holding capacitors 11A and IIB and the voltages at the output terminals of the sample and hold circuits 20OA and 200B, ζ, will remain constant even if the input signal l or reference signal 2 changes. By repeating these steps, differential amplification with an auto-zero machine and sample-and-hold function is performed.Problems to be Solved by the InventionAs can be seen from FIG. Even if auto-zero operation is necessary, due to leakage current, the offset holding capacitor 10A and the voltage held in IOB will change over time, so it is necessary to perform auto-zero operation more frequently than a certain level. amplifier 100
Operating current (upper: Determined by current source 7; increasing it will increase power consumption; decreasing it will cause MOS)
The present invention (above) was made as a result of devising and researching the drawbacks of the above-mentioned differential amplifier with a sample and hold function, which had the problem that the time required for auto-zero operation was longer due to the smaller current flowing through the transistors 5A and 5B. It is an object of the present invention to provide a differential amplifier with a sample and hold function that is faster than the conventional one.
An input signal connected to one input terminal of the differential amplifier through a switch, a reference signal connected to the other input terminal of the differential amplifier, and two input terminals of the differential amplifier connected to each other. two sample-and-hold circuits whose inputs are respective output terminals of the differential amplifier; and two switches which respectively connect the output terminals of the two sample-and-hold circuits and the voltage source. Each of the two sample and hold circuits is composed of a switch and an offset voltage holding capacitor and a differential voltage holding capacitor connected to the switch, and causes the differential amplifier to perform an auto-zero operation from when the two sample and hold circuits are in the hold state. An auto-zero device characterized by the above-mentioned auto-zero device which also works in a differential amplifier with a sample-and-hold function. By causing the dynamic amplifier to perform auto-zero operation, the time for auto-zero operation is apparently shorter. Therefore, a faster auto-zero device than the conventional differential amplifier with a sample and hold function can be obtained. Auto-zero unit The configuration of the differential amplifier with sample and hold function is shown, and its timing is shown in Figure 2.

The configuration shown in Figure 1 is the same as the conventional configuration, and in order to perform accurate differential amplification, the jL offset voltage must be removed (1 Auto-zero machine in Figure 1 Amplification of the difference between input signal 1 and reference signal 2 using a differential amplifier with sample and hold function (upper
Follow the steps below:

Step 1 (Auto zero) Even though switch 4 is already closed and switch 3 is open, the offset voltage of the differential amplifier 100 appears at the output terminal of the differential amplifier 100. , 8& By closing the switches 12A, 12B, the offset voltage holding capacity 10A, I
In OB, even if the offset voltage of the differential amplifier 100 is held, Step 2 (sample) Next, if switch 4 is opened and switch 3 is closed,
A voltage obtained by adding an offset voltage to the voltage obtained by amplifying the difference between input signal 1 and reference signal 2 appears at the output terminal of the differential amplifier 100. In this case, when switches 8A and 8B are closed, when switches 12A and 12B are opened. A voltage obtained by amplifying the difference between input signal 1 and reference signal 2 appears at the output terminals of sample and hold circuits 20OA and 200B.
Since the offset voltage of the differential amplifier 100 is still held, the voltage appearing at the output terminals of the sample and hold circuits 200A and 200B does not include the offset voltage of the differential amplifier 100.Step 3 (Hold) Then, switch 8A, 8B. Then, the voltage of the differential voltage holding capacitor 11A and IIB and the voltage of the output terminal of the sample and hold circuits 20OA and 200B (upper) will be kept constant even if the input signal 1 or reference signal 2 changes. By opening switch 3 and closing switch 4, even if the differential amplifier 100 is already in auto-zero operation while the sample-and-hold circuits 20OA and 200B are in hold operation, repeating these operations will cause Even if differential amplification with auto-zero function and sample-hold function is performed, the offset voltage holding capacitance is 10% during auto-zero operation.
A, 10B is made to hold the offset voltage of the differential amplifier 100. In other words, the force t to charge with that voltage is then
At the same time, it is necessary to charge the parasitic capacitances existing in the drains of MOS transistors 5A and 5B, resistors 6A and 6 & switches 8A and 8B, and the wiring that connects them to L.And even though the charging current is determined by the current source 7, Therefore, the time required for auto-zero is also determined. In the present invention (as described above, even if the differential amplifier 100 is already in auto-zero operation while the sample-and-hold circuits 200A and 200B are performing the hold operation, the drains of the transistors 5A and 5B, Resistor 6A, 6 & Switch 8A, 8 &
The offset voltage of the differential amplifier lOO has already been charged by 1 in the parasitic capacitance existing in the wiring section that drives them. Therefore, at the time of auto-zero in step 1 above,
It is only necessary to charge the offset voltage holding capacitor 10A, IOB, and it takes only a short time. As a result, a differential amplifier with a high-speed auto-zero mechanism and sample-and-hold function can be obtained.As shown in FIG.
In the case of a configuration in which 0 is inserted, the load on the differential amplifier 100 is lighter than that by inserting the buffer amplifier 50 in the above method.It is also possible to obtain a differential amplifier with a faster auto-zero function and sample-hold function. Effects of the Invention As is clear from the above explanation, the speed of the differential amplifier with auto-zero mechanism and sample-hold function can be greatly increased by changing the C'L timing slightly. Therefore, the present invention is extremely useful. Deamo

[Brief explanation of drawings]

Figure 1 shows the configuration of the auto-zero mechanism of the present invention and the conventional auto-zero mechanism. Figure 2 shows the configuration of the auto-zero mechanism of the present invention. The timing of the differential amplifier with sample-and-hold function. Figure 3 shows the auto-zero mechanism of the present invention. Other configurations of the differential amplifier with hold function are as follows.
The figure is a timing diagram of a conventional auto-zero mechanism differential amplifier with sample and hold function.1... Input multiplication 2... Reference signal! 3.4.8A
, 8B, 12A, 12B...Switch, IOA, I
OB...Offset voltage holding capacitor tlIA, 11B
...Operating voltage holding capacity, 100...Differential amplification t
20OA, 200B...Sample hold cycle

Claims (1)

[Claims] a differential amplifier; an input signal connected to one input terminal of the differential amplifier via a switch; a reference signal connected to the other input terminal of the differential amplifier; two sample-and-hold circuits whose inputs are the respective output terminals of the differential amplifier; and two switches which respectively connect the output terminals of the two sample-and-hold circuits and the voltage source. The two sample-and-hold circuits each include a switch and an offset voltage holding capacitor and a differential voltage holding capacitor connected to the switch, and the difference between the two sample-and-hold circuits is in the hold state. A differential amplifier with an auto-zero function and a sample-hold function that allows the dynamic amplifier to perform auto-zero operation.