JP2725424B2 - Analog-to-digital converter - Google Patents

Description

The present invention relates to an analog-to-digital converter (hereinafter, referred to as an A / D converter) using a chopper amplifier, and more particularly to a timing control method thereof.

[Conventional technology]

FIGS. 2 and 3 show a configuration block diagram and an operation waveform diagram of an A / D converter using a conventional chopper amplifier. In FIG. 2, AN _{1 to} AN _n are a plurality of analog inputs, SEL ₁ to
SEL _n is an input select signal and an input select switch for selecting one of a plurality of analog inputs, SAMP is an input sampling signal and an input sampling switch for inputting an analog input to the comparator 4, and 3 is a reference for comparison. D / a converter for generating a voltage, 4 comparators chopper amplifier system, T _B is the input bias signal for biasing the chopper amplifier stages, 5 in the comparator output, to the latch or register (not shown) Is done.

Next, the operation will be described. As shown in the waveform diagram of FIG. 3, the analog input select signal SEL _i remains between "H" to which the terminal is selected. While the SAMP signal is “H”, the analog input is taken in and transmitted to the input 2 of the comparator 4. Period of time between the SAMP signal is "H", that is, biased chopper amplifier each stage during the chopper amplifier bias signal T _B is "H", moves to the operating point of the gain of the amplifier is maximized. Chopper amplifier bias signal T _B is made to be "L" before the SAMP signal is "L" as shown in Figure 3. Next, the SAMP signal is “L”,
▼ When the signal becomes “H”, the output of the D / A converter 3 becomes the comparator 4
And the magnitude relationship with the analog input signal is compared. The signal 5 indicating the result of this comparison is input to the next-stage latch circuit or register circuit and becomes a converted digital value.

[Problems to be solved by the invention]

Since the conventional A / D converter was configured as described above, for example, SA from T _B signals as shown in Figure 3 is turned off
If the MP signal is superposed variation due to noise or the like in the analog input to the period until the off, it is transmitted as it is until the comparator input, the period chopper amplifier bias signal T _B is chopper amplifier because it off operable State
The fluctuation of the input at point 2 causes the chopper amplifier to operate, deviating from the normal bias point, and then SAMP
When the signal is turned off, the reference voltage is input from the D / A converter. However, since the operating point of the chopper amplifier is shifted, there is a problem that the conversion accuracy is deteriorated as a result.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a stable A / D converter in which accuracy does not deteriorate with respect to fluctuation due to analog input noise or the like.

[Means for solving the problem]

An A / D converter according to the present invention is configured such that a select switch for selecting one analog input from a plurality of analog inputs, a sampling switch for sampling the selected analog input, and a sampled analog input are input, It has a multi-stage chopper amplifier,
A comparator is provided in which a bias signal for each stage of the chopper amplifier is provided for a certain period of time during which the analog input is being sampled and before the end of sampling, and the selected analog input is provided with a bias signal for the chopper amplifier. It is characterized in that it is turned off until the analog input sampling is completed after it is no longer possible.

[Action]

According to the present invention, the selected analog input is turned off from the time when the bias signal to the chopper amplifier is no longer supplied to the end of the sampling of the analog input. No fluctuation is transmitted to the comparator input even if the fluctuation is superimposed.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an operation waveform diagram of an A / D converter according to an embodiment of the present invention. The configuration block diagram of the A / D converter is the same as that of FIG.

In this embodiment, the analog input select signal
The SEL _i, chopper amplifier bias signal T _B from becomes "L" to the sampling end of the analog input, i.e. input sampling signal SAMP is are to be the "L" period until the "L". As a result, even if a change due to noise or the like is superimposed on the analog input after the end of the chopper amplifier bias period, the change is not transmitted to the comparator input 2, and stable conversion with high accuracy can be performed.

〔The invention's effect〕

As described above, according to the present invention, since the analog input select signal is turned off only during the period that is susceptible to input fluctuations due to noise or the like, a highly accurate and stable A / D converter can be obtained.

[Brief description of the drawings]

FIG. 1 is a control timing waveform diagram of an A / D converter according to one embodiment of the present invention, and FIG.
FIG. 3 is a block diagram of a configuration of a D converter, and FIG. 3 is a timing chart of control timings of a conventional A / D converter. AN _i : analog input, SEL _i : analog input select signal, SAMP: input sampling signal, T _B : chopper amplifier bias signal, 2: comparator input, 3: D / A converter, 4: comparator, 5: comparison Output.

Claims (2)

(57) [Claims] 1. A select switch for selecting one analog input from a plurality of analog inputs, a sampling switch for sampling a selected analog input, and a sampled analog input and a plurality of stages of chopper amplifiers. A comparator for providing a bias signal to the chopper amplifier of each stage for a fixed period of time during which the analog input is being sampled and before the end of the sampling, and wherein the selected analog input is biased with respect to the chopper amplifier. An analog-to-digital converter characterized by being turned off from the time when a signal is not supplied until the end of the sampling of the analog input. 2. A select switch for selecting one analog input from a plurality of analog inputs, a sampling switch adapted to sample the selected analog input and to switch between the selected analog input and a reference voltage for comparison. A switch and a sampled analog input or a switched comparison reference voltage are input, and a plurality of stages of chopper amplifiers are provided. A comparator that is provided for a fixed period of time before the end and outputs a comparison signal between the sampled analog input and the reference voltage for comparison, wherein the selected analog input is a bias signal to the chopper amplifier. After it is no longer given Serial analog-to-digital converter, characterized in that so as to turn off until the sampling end of the analog input.