JPH04124914A - Control signal setting system in chopper amplifier - Google Patents

Abstract

PURPOSE:To reduce the deterioration of precision against the variation of supply voltage or a noise by setting a chopper control signal so that the potential amplitude of the chopper control signal to be impressed to the gate of a transistor has a period shorter than the difference of the current potential of an inverter and earth potential during the shortcircuit period of the input point and the output point of the inverter. CONSTITUTION:The chopper control signal Tc is set so that the potential amplitude of the chopper control signal Tc has the period shorter than the difference of the supply potential Vcc of the inverter 1 and the earth potential during the shortcircuit period of the input point 7 and the output point 8 of the inverter 1. In case that the variation arises in the supply voltage Vcc, since the gate potential of a chopper transistor 2 is V1 (V1<Vcc), impedance is high, and a signal feedback function from the output point 8 to the input point 7 becomes very small, and it becomes the feedback function V'7 ( V'7<< V7). Thus, since offset quantity at the time when the chopper control signal Tc is disconnected is very small, in case that afterwards, a signal to be amplified is transmitted to the input point 7, it can be amplified at good precision.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an analog-to-digital converter (hereinafter referred to as A/D converter).
The present invention relates to an operating potential setting method in a chipper type amplifier (hereinafter referred to as a chopper amplifier) used for a converter, a comparator, etc.

[Conventional technology]

A successive approximation type A/D converter operates at relatively high speed,
Moreover, it is used because it has a compact shape.A chopper amplifier is used in the comparator part of the A/D converter of this method, and the performance of the chopper amplifier is the overall performance of the A/D converter. This is the main factor determining performance.

Of course, the primary performance of an A/D converter is related to accuracy, such as linearity error, differential linearity error, offset error, full-scale error, and absolute accuracy, but other than that, Another very important characteristic is environmental resistance, that is, less deterioration of accuracy due to power supply voltage fluctuations or noise application.

The configuration and basic operation of a conventional chopper amplifier are shown in Figs. 5, 6, and 7. In the figures, l is an inverter for amplifying the input signal, and 2 is an inverter 1 at the operating point as an amplifier. Chop transistor for use, 3
is a chopper control signal line through which a chopper control signal applied to the gate of chopping transistor 2 flows; 4 is one stage of chopper amplifier composed of inverter 1 and transistor 2; 5 and 6 are capacitors for input coupling; 8
are the input point and output point of the inverter 1, respectively. The chopping transistor 2 has a source and a drain connected to the input point 7 and the output point 8 of the inverter 1, respectively, and shorts the input point 7 and the output point 8 of the inverter 1 for a certain period of time according to a chopper control signal applied to the gate. The chopper amplifiers 4 are cascaded in the required number of stages according to the required performance. 9 is a control signal generation circuit that generates a chopper control signal.

Next, the operation will be explained. When the chopper control signal Tc on the chopper control signal line 3 is active, that is, at the power supply potential ycc level in this case (period I), the input point 7 and the output point 8 of the inverter 1 are short-circuited. In other words, as can be seen from the input/output characteristics in Figure 6, input point 7 and output point 8
are biased together at approximately 2VCC, placing inverter 1 at its maximum gain point as an amplifier. Thereafter, when the chopper control signal TC is turned off, that is, becomes the Vas level, the input point 7 and the output point 8 become separated. At this time, if there is a potential change in the front stage of the input coupling capacitor 5,
The potential change is transmitted to the input point 7 of the inverter 1, and in response, the output point 8 of the inverter 1 outputs "H" (high level) or "L" (low level). For example, when input point 7 changes to "H" side, output point 8 becomes "L"
When the input point 7 changes to the "L" side, the output point 8 changes to the "H" side (period ■).

[Problem to be solved by the invention]

Since the conventional chopper amplifier has the above-described configuration, it has the disadvantage that accuracy tends to deteriorate due to fluctuations in the power supply voltage. This will be explained using FIG. At a certain time during which the chopper control signal TC is active 1. When the power supply voltage VCC fluctuates as shown in the figure, the output point 8 is the output of the inverter 1, so the potential changes according to the fluctuation of the power supply voltage V, (.When the chopper control signal Tc is "H", the inverter 1 Since input point 7 and output point 8 of .

Here, when the chopper control signal TC is turned off, the coupling between the input point 7 and the output point 8 is eliminated, and the input point 7 enters a high impedance state, so that the fluctuation of ΔV is maintained as it is.

Output point 8 receives the voltage at input point 7 and converts it to inverter l.
is amplified and the potential is V. It decreases towards. As described above, even after the chopper control signal Tc is cut off, the offset voltage Δ■7 is still applied to the input point 7 of the inverter 1, so the signal that should be amplified is then transmitted to the input point 7. However, it will not be possible to amplify correctly even if
This will result in deterioration of accuracy.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a control signal setting method for a chopper amplifier in which accuracy is less likely to deteriorate due to power supply voltage fluctuations and noise.

[Means to solve the problem]

The control signal setting method in the chopper amplifier according to the present invention is such that during the short-circuit period between the input point 7 and the output point 8 of the inverter 1, the potential amplitude of the chopper control signal Tc applied to the gate of the transistor 2 is set to the power supply potential V of the inverter 1. The chopper control signal Tc is set by the potential setting means 10 so as to have a period smaller than the difference between cc and the ground potential.

[Effect]

The chopper control signal Tc applied to the gate of the transistor 2 during the short-circuit period between the input point 7 and the output point 8 of the inverter 1 has a period in which the potential amplitude is smaller than the difference between the power supply potential ■cc of the inverter 1 and the ground potential. It is set by the potential setting means 10 as follows. This makes it difficult for fluctuations on the output point 8 side of the inverter 1 to be fed back to the input point 7 side.

〔Example〕

FIG. 1 is a configuration diagram of a chopper amplifier according to an embodiment of the present invention, FIG. 2 is an input/output characteristic diagram of the inverter in FIG. 1,
FIG. 3 is a signal waveform diagram showing the relationship between the chopper control signal and the output point signal in this embodiment. Figures 1 to 3
In the figure, components corresponding to those shown in FIGS. 5 to 7 are denoted by the same reference numerals, and their explanations will be omitted. 1st
In the figure, 10 indicates input point 7 and output point 8 of inverter 1.
During the short-circuit period, the chopper control signal Tc is set so that the potential amplitude of the chopper control iB (No. 8 Tc) applied to the gate of the transistor 2 has a period smaller than the difference between the power supply potential Vcc and the ground potential of the The control signal logic circuit 9 is a potential setting means 10 for controlling the potential setting means 1.
0 output, the chopper control signal T as shown in FIG.
Generates 0. The chopper control signal Tc is kept at a potential V r (V + <Vcc) that is lower than the power supply voltage ■ cc for a certain period (■) of the active period (■). Of course, this potential (1) must have a level necessary to short-circuit the output of the chopper amplifier 4 (the input point 7 and the output point 8 of the input terminal 7N/-1). The basic operation of this embodiment is the same as in the conventional example, in which the Chiyo-Sova amplifier 4 is brought to the maximum gain point in period (3), and is operated as an amplifier in period (2).

Next, the operation when a fluctuation occurs in the power supply voltage ycc will be explained using FIG. Time 1. When the power supply voltage Vcc fluctuates as shown in the figure, the potential at the output point 8 changes in accordance with the fluctuation of the power supply voltage Vcc, as in the conventional example. At this time, the gate potential of chop transistor 2 is 'J
I (V+<V.,), the impedance is high, and the amount of signal feedback from the output point 8 to the input point 7 is extremely small, and the amount of feedback at time t2 is Δ■7°(Δy,'
<<Δv,). In this way, the chopper control signal Tc
Since the amount of offset when the signal is cut off is very small, when a signal to be amplified is subsequently transmitted to the input point 7, it is possible to amplify it with high accuracy.

In this way, the chopper amplifier of the above embodiment changes the potential amplitude of the chopper control signal Tc during the period (3), which is susceptible to fluctuations in the power supply voltage and noise, so that fluctuations at the output point 8 are transferred to the input point 7. It is less likely to be backed up, and the input signal can be amplified with high precision even in bad environments.

Incidentally, in the above embodiment, the time period during which the chopper control signal Tc is given the potential ■ is a part of the total active period l, but the period during which the potential ■1 is applied is the total active period I. may be the same as

Further, it is not necessary to apply this chopper control signal to all stages of the chopper amplifier, and the same effect can be obtained even if it is applied to only a part of the chopper amplifier including the first stage.

Further, in this embodiment, the chopping transistor is an N-channel transistor, but it may be a P-channel transistor or an N-channel transistor.

Even in the case of using both P-channel transistors, it is possible to obtain the same effect using the same concept and method as in this embodiment.

(Effects of the Invention) As described above, according to the present invention, during the short-circuit period between the input point and the output point of the inverter, the potential amplitude of the chopper control signal applied to the gate of the transistor is the difference between the power supply potential and the ground potential of the inverter. Since the chopper control signal is set to have a period smaller than As a result, fluctuations in the output point of the inverter are less likely to be fed back to the input point, and therefore, it is possible to provide a chopper amplifier with less deterioration in accuracy due to fluctuations in power supply voltage and noise.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a chopper amplifier according to an embodiment of the present invention, FIG. 2 is an input/output characteristic diagram of the inverter in FIG. 1,
Fig. 3 is a signal waveform diagram showing the relationship between the chopper control signal and the output point signal in this embodiment, Fig. 4 is a signal waveform diagram for explaining the operation of this embodiment, and Fig. 5 is a signal waveform diagram of the conventional chopper. The amplifier configuration diagram, Figure 6 is the input/output characteristic diagram of the inverter in Figure 5, Figure 7 is a signal waveform diagram showing the relationship between the chopper control signal and the output point signal in this conventional example, and Figure 8 is the signal waveform diagram showing the relationship between the chopper control signal and the output point signal in this conventional example. FIG. 3 is a signal waveform diagram for explaining problems in the conventional example. 1... Inverter, 2... Transistor, 4...
Chopper amplifier, 7...Input point, 8...Output point, 9
... Control signal generation circuit, 10... Potential setting means, T
c...Chopper control signal. Agent Patent Attorney Jun Miyazono No. 30 Figure 4

Claims (1)

[Claims] an inverter for amplifying an input signal; and a source and drain connected to the input and output points of the inverter, respectively, for short-circuiting the input and output points of the inverter for a certain period of time according to a chopper control signal applied to the gate. In a chopper amplifier comprising a transistor, during a short-circuit period between an input point and an output point of the inverter, a potential amplitude of a chopper control signal applied to the gate of the transistor is smaller than a difference between a power supply potential and a ground potential of the inverter. A control signal setting method for a chopper amplifier, characterized in that the chopper control signal is set to have a period.