JPH07273650A - A/d converter circuit for nonlinear signal - Google Patents

Abstract

PURPOSE:To obtain an A/D converter circuit with high resolution with respect to a wide signal level range of a nonlinear input signal. CONSTITUTION:A changeover circuit 3 is used to switch a path between an output of an amplifier group 2 and an input terminal of an A/D converter 4 from an amplifier 2x with a higher gain toward an amplifier 2x-1 with a lower gain sequentially to retrieve an amplifier 2i with an optimum gain. A sample- and-hold circuit 1 holds an analog input signal and the A/D converter 4 converts an amplified signal of the amplifier 2 into digital data. An overflow detection section 5 inspects whether or not the digital data overflows. A gain control section 6 receives an overflow signal and any of connection parts 3a-3x of the connection circuit 3 is sequentially revised to select the amplifier 2i by which no overflow signal is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an A / D for nonlinear signals.
Regarding a conversion circuit, particularly in a measurement data processing circuit, a nonlinear analog signal can be converted into analog / digital (A
/ D) A / D conversion circuit for conversion.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an A / D conversion circuit for a non-linear signal generally has a fixed gain input amplifier and an A / D conversion circuit.
It is composed of a D converter. The gain of the input amplifier is
The maximum value of the measurement range of the input analog signal is A / D
It is determined to match the full scale of the transformation. According to this setting, the resolution per bit is the measurement range and A
It will be determined depending on the linearity of the input signal characteristics in addition to the number of bits of the / D converter.

As an example of the prior art relating to the A / D converter,
The one disclosed in Japanese Patent Laid-Open No. 61-248622 has a structure in which an analog input signal is divided into a plurality of stages, level-shifted and amplified, and an A / D converter with a low bit number is used for each stage to increase the It constitutes an A / D converter of the number of bits.

Further, in the one disclosed in Japanese Patent Laid-Open No. 162162/1989, when the input signal is smaller than a predetermined value, the gain of the amplifier is increased, the input signal is increased, and the input signal is increased. The number of bits of the output data of is shifted to the lower order. This method improves the conversion accuracy of low-level signals.

[0005]

However, in the conventional A / D conversion circuit, since the nonlinear input signal is A / D converted, the resolution per bit greatly differs depending on the characteristics of the input signal as described above. Therefore, there is a problem that a high-resolution range and a low-resolution range occur in the input signal area regardless of the design specifications. A specific example of the content of this problem will be described with respect to the temperature sensor.

FIG. 3 shows an example of resistance and output voltage characteristics of a general temperature sensor. The graph shown by the solid line in the figure shows the characteristics detected as a voltage signal by configuring the above temperature sensor in a Wheatstone bridge circuit (not shown). The Wheatstone bridge circuit, which has excellent linear characteristics, detects a voltage value that is approximately proportional to the resistance change of the sensor.

The temperature resistance characteristic of this temperature sensor has high sensitivity in a low temperature portion and a large inclination angle of the characteristic curve. That is, the sensitivity of the sensor is high and the resolution per output voltage is high. However, the slope of the characteristic curve becomes more gradual as the temperature becomes higher. That is, the sensitivity of the sensor is low and the resolution per output voltage is low. As described above, the general temperature sensor has different sensitivity characteristics between the low temperature portion and the high temperature portion.

When converting the voltage signal corresponding to the above temperature data into a digital signal, the temperature resolution is extremely different between the low temperature portion and the high temperature portion. The wider the measurement range,
This tendency is remarkable. Therefore, it is difficult to obtain a wide measurement range and highly accurate measurement characteristics at the same time with the conventional circuit configuration. Therefore, the resolution of the portion where the voltage change is small, that is, the portion where the resistance does not change much even if the temperature changes greatly, is sacrificed, or the detection range is narrowed and a measurement circuit that sacrifices the measurement range is assembled.

As described above, in the A / D conversion circuit using a non-linear signal as an input signal, it is difficult to obtain sufficient characteristics or desired data because the A / D conversion circuit composes a circuit in which the measurement range or resolution is compromised to some extent. Is in a state.

An object of the present invention is to provide an A / D conversion circuit which can obtain high resolution over a wide signal level range of a non-linear input signal.

[0011]

In order to achieve the above object, an A / D conversion circuit for a nonlinear signal according to the present invention includes a plurality of amplifying means having different gains, and any one of the amplifying means.
A switching means for connecting the output of the A / D conversion means to the analog signal input terminal of the A / D conversion means, a signal level detection means for detecting the signal level of the digital output signal of the A / D conversion means, and a signal level detection means. It has a gain control means for outputting a switching signal for switching the connection of the switching means in accordance with the magnitude of the detected signal level, and a signal level output means for outputting the signal detected by the signal level detecting means together with a digital signal. It is characterized by that.

Further, the signal amplifying means is preferably arranged more finely than a portion having a high signal sensitivity for amplifying a portion having a low signal sensitivity of the nonlinear signal so as to amplify the nonlinear signal.

Further, by adjusting the sensitivity of each of the signal amplifying means, the analog signal input to the analog input terminal of the A / D converting means may be corrected to a more linear signal.

[0014]

Therefore, according to the A / D conversion circuit for the non-linear signal of the present invention, the signal level of the digital output signal is detected, and the amplified signal having a different gain is detected according to the detected signal level. Since the converter is connected to the input terminal of the analog signal, it is possible to set an amplifier having a different gain depending on the signal level of the input signal.

[0015]

Embodiments of the A / D conversion circuit for a nonlinear signal according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown an embodiment of an A / D conversion circuit for nonlinear signals of the present invention.

(First Embodiment) The A / D converter of FIG.
A / D for non-linear signals such as thermistors with temperature resistance characteristics
It shows a configuration example for conversion. The A / D conversion unit includes a sample hold circuit 1 for temporarily holding a nonlinear input signal, a plurality of stages of amplifiers 2, a switching circuit 3, an A / D converter 4,
The overflow detection circuit 5, the gain control unit 6, and the gain flag output unit 7 are included. The input signal is
The sensor is composed of a fixed resistor and a Wheatstone bridge (not shown), and a voltage signal proportional to a change in the resistance value of the sensor is obtained as an output signal.

The sample and hold circuit 1 is a circuit section for temporarily holding an input signal in order to stably execute the A / D conversion operation. The amplifier 2 is composed of X amplifiers 2a, 2b, ..., 2x having different gains. The gain characteristic and the number of stages X are set according to the characteristics of the nonlinear input signal, the desired accuracy, and the like. The switching circuit 3 is a switch for selecting any one of the outputs of the plurality of amplifiers 2 and switching the connection to the next stage, and has the number of circuits corresponding to the stage number X of the amplifiers. An analog switch is used as the type of switch in the embodiment. This switching circuit 3a, 3b,
The switching control terminals of 3x are connected to the gain control section 6 to control the switching operation.

The A / D converter 4 is a circuit section for converting an analog signal into a digital signal. Input terminal is switching circuit 3
Are connected in parallel with the respective output terminals of
It is connected to the / D data output section and also to the overflow detection section 5. The A / D conversion method and the number of output bits are not limited.

The overflow detection section 5 is a circuit section for monitoring the state of the digital signal converted by the A / D converter 4 and outputting a flag when the predetermined state is reached. In the embodiment, the flag is set when the digital signal is all "1" (FFH). The flag is output to the gain control unit 6 and the gain flag output unit 7.

The gain control section 6 is a circuit section for outputting a gain control signal based on the state of the flag output from the overflow detection section 5. The flag control signal output from the gain control unit 6 is connected to the switching control terminal of the switching circuit 3.

The gain flag output section 7 includes a gain control section 6
It is a circuit unit that outputs a flag for identifying the switching state of the gain due to. This signal is output together with the A / D data 8 and used for recognizing the gain state of the amplifier 2 in a unit (not shown) that processes the received A / D data 8.

The relationship between the gain of the amplifier 2 and the switching circuit 3 and the gain control section 6 is shown by, for example, the amplifier 2a, the amplifier 2b ,.
A description will be given in the case where the amplifier 2x and the X-stage amplifier 2 whose gain is sequentially increased are used.

At the beginning of the measurement, the amplifier 2x having the highest gain of the amplifier 2 is sequentially switched to the amplifier 2i having the lower gain to search for the amplifier having the optimum gain. First, the analog input signal is held by the sample hall circuit 1, the sampled and held analog signal is amplified by the amplifier 2x at the highest stage, and converted into digital data by the A / D converter 4 via the switching circuit 3. .

The overflow detection unit 5 checks whether or not the digital data has overflowed.
When the overflow occurs, the gain control unit 6 receives the overflow signal and outputs a control signal to connect the amplifier 2x at the highest stage to the amplifier 2x-1 at the stage lower by one stage and the A / D converter. To change the connection of the switching circuit.
After changing the stage of the amplifier, the overflow detector 5 checks the digital data again. If the output of the digital signal of the A / D converter 4 does not overflow due to the connection with the uppermost amplifier 2x, the amplifier 2x and A
Holds the connection state with the / D converter.

The above-mentioned checks in the overflow detection unit 5 are sequentially executed, and the connection of the connection circuit is sequentially changed to the amplifier one stage lower until the overflow flag in the overflow detection unit 5 disappears. In addition, the overflow flag in the process of selecting the amplifier of the optimum stage is sequentially output from the gain flag output unit 7 together with the digital data. When the overflow flag is output when the amplifier with the lowest gain is selected, the input signal is excessive and it is necessary to reduce the input signal.

In the above embodiment, the input signal of the A / D converter 4 is shifted from a high gain side having a plurality of different gains to a low gain side. However, even if it is sequentially shifted from a low gain side to a high gain side. good. In this case, the amplifier with the gain immediately before the overflow flag is set is selected as the optimum amplifier.

(Second Embodiment) In the second embodiment, the overflow detection unit 5 performs two types of checks, an overflow state and an underflow state, and outputs these identification flags. The conditions for outputting the overflow flag are the same as in the case of the first embodiment. The output condition of the underflow flag is, for example, 1/2 or less of the full scale of the A / D converter 4 is output. If this output condition is taken into consideration by dividing the number of stages of the amplifier and the low-sensitivity range of the sensor finely and roughly dividing the high-sensitivity range, better results can be obtained in improving the linearity of the sensor. To be This embodiment will be described with reference to FIG.

The gain controller 6 receives the above-mentioned two types of flags and controls the switching of the switching circuit 3. The other structure is the same as that of the first embodiment. In the operating state,
In the second embodiment, the measurement is started from the amplifier of a predetermined stage. For this grade, it is also possible to use the final grade of the previous measurement. However, you may start from the amplifier of the lowest gain like 1st Example. In the embodiment, the measurement is started from the amplifier 2i at a predetermined stage.

The analog input signal is held by the sample hall circuit, the analog signal sampled and held by the amplifier 2i at a predetermined stage is amplified, and the analog signal is passed through the switching circuit 3i to A /
The D converter 4 converts the digital data. The overflow detection unit 5 checks whether the digital data has overflowed or underflowed. When it overflows, it outputs a control signal to switch to a low gain amplifier, and when it underflows, it switches to a high gain amplifier. This switching control is controlled so that neither the overflow flag nor the underflow flag is output from the overflow detection unit 5.

When the overflow flag is output in the selected state of the amplifier with the lowest gain, the input signal is excessive, and when the underflow flag is output in the selected state of the amplifier with the highest gain, the input signal is input. The signal is too low.

The A / D conversion circuit of the second embodiment has flexibility in the selection operation of the optimum amplifier, for example, step jump, series converging, etc., so that it may be used when the input signal fluctuates or is tracked for a long time. It is possible to handle various measurements.

In the A / D conversion of the above-mentioned embodiment, the input amplifiers having a plurality of different gains are automatically switched in accordance with the input level of the signal, so that even a nonlinear signal having a wide measurement range is relatively constant. A / D conversion can be realized relatively easily with resolution. Also, when you want to obtain data in a wide measurement range and at the same time obtain a specific range with high resolution, you can set the relationship between the gain of the amplifier and the measurement range appropriately to set any measurement range to a desired resolution. It becomes possible to set.

Although the above-described embodiment is a preferred embodiment of the present invention, the present invention is not limited to this and various modifications can be made without departing from the gist of the present invention.

[0034]

As is apparent from the above description, the A / D conversion circuit for nonlinear signals according to the present invention A / D converts an amplified signal having a different gain according to the signal level of the digital output signal. In order to connect to the analog signal input terminal of the means, an amplifier having a different gain is set according to the signal level of the input signal. Therefore, a non-linear input signal having different characteristics depending on the level can be corrected by an amplifier having a different gain.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of an A / D conversion circuit for nonlinear signals of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a conventional A / D conversion circuit for nonlinear signals.

FIG. 3 is a diagram showing a form example of a non-linear input signal.

[Explanation of symbols]

 1 sample hold circuit 2 amplifier 3 switching circuit 4 A / D converter 5 overflow detector 6 gain control unit 7 gain flag output unit 8 A / D data 9 flag

Claims (3)

[Claims] 1. A plurality of amplification means having different gains, a switching means for connecting an output of any one of the amplification means to an analog signal input terminal of the A / D conversion means, and the A / D conversion. Signal level detecting means for detecting a signal level of a digital output signal of the means, and a gain for outputting a switching signal for switching the connection of the switching means according to the magnitude of the signal level detected by the signal level detecting means. An A / D conversion circuit for a non-linear signal, comprising: control means and signal level output means for outputting the signal detected by the signal level detection means together with the digital signal. 2. The non-linear signal amplifier according to claim 1, wherein the signal amplifying means is arranged more finely than a high signal sensitivity region for amplifying a low signal sensitivity region of the non-linear signal and amplifies the non-linear signal. A / D conversion circuit for signals. 3. An analog signal input to an analog input terminal of the A / D conversion means is corrected to a more linear signal by adjusting the sensitivity of each of the signal amplification means. A / D for nonlinear signal according to 2
Conversion circuit.