JPH0513404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for evaluating and measuring AC characteristics in an oversampling type analog-to-digital (A/D) converter with multiple bit output.

(Prior Art) Conventionally, when trying to evaluate and measure AC characteristics such as signal-to-noise ratio (S/N) in an oversampling type A/D converter using an analog measuring instrument, the oversampling The output digital signal of the A/D converter is passed through a speed converting digital filter to reduce its sampling speed, and then converted into an analog signal using a digital-to-analog (D/A) converter. This was done using a signal obtained through an analog filter with a passband characteristic.

(Problems to be Solved by the Invention) According to the above method, the digital filter for speed conversion reduces the sampling speed, so a low speed D/A converter can be used, but on the other hand, there is no deterioration in accuracy. In order to reduce the sampling speed, it is necessary to increase the number of bits of the digital signal, which increases the hardware size of the speed conversion digital filter and requires a multi-bit D/A converter. There was a problem.

The present invention eliminates the above-mentioned problems and measures the AC characteristics of an oversampling type A/D converter by obtaining an analog signal by simple means without using a digital filter for speed conversion or a D/A converter. The purpose is to provide a method.

(Means for Solving the Problem) In order to solve the above problem, the present invention uses an oversampling type A that converts the output digital signal of an oversampling type A/D converter with multiple bit output into an analog signal and measures it. In the method for measuring the AC characteristics of a /D converter, each of the multiple-bit digital signals output from the oversampling type A/D converter at each sampling period is decoded, and the pulse width of each decoded output is adjusted according to the numerical value. 2 signals of 1 bit by outputting them on the same signal line at fixed time intervals.
The 1-bit binary signal is converted into an analog signal through an analog filter that passes only signals in the measurement band, and AC characteristics are measured from the analog signal.

(Function) According to the present invention, oversampling type A/
A multi-bit digital signal output from a D converter is decoded into one of 2 n signals, where ⁿ is the number of bits, and then decoded into one of 2 ⁿ signals according to its numerical value. It is converted into a signal with a pulse width, outputted on the same signal line at regular time intervals, converted into a 1-bit binary signal, and then converted into an analog signal by an analog filter that passes only the band necessary for measurement. The analog signal is converted into a signal, and the AC characteristics of the oversampling type A/D converter are measured from the analog signal.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which 1 is an input terminal, 2 is an oversampling type A/D converter (hereinafter referred to as A/D converter), 3
is an encoder circuit, 4 is a multiplexer, and 5 is an analog low-pass filter (hereinafter referred to as analog LPF).
It is called. ), 6 is a clock generator, 7 is a frequency divider, 8
is a pulse generator, and 9 is an output terminal.

The A/D converter 2 is a target for evaluation and measurement, and converts the analog signal input from the input terminal 1 into a plurality of, for example, n-bit digital signals.

The encoding circuit 3 decodes the n-bit digital signal into 2 ⁿ signals, and weights each of the 2 ⁿ signals according to its numerical value, as will be described later.

The multiplexer 4 is a well-known type having 2 ⁿ input terminals and 1 output terminal, and time-division multiplexes the weighted signals to form one bit (line).
signal.

The analog LPF 5 limits the signal band at a predetermined cutoff frequency c in order to evaluate and measure the AC characteristics of the A/D converter 2, and converts the 1-bit signal to an analog signal with a frequency of c or less. , is sent to output terminal 9. Furthermore, this analog
LPF5 is also used in conventional measurement methods.

Clock generator 6 generates clock pulses P1 and P2 of frequencies 1 and 2, sends clock pulse P1 to frequency divider 7, and sends clock pulse P2 to pulse generator 8. Here, the phases of clock pulses P1 and P2 are synchronized, and their frequencies 1 and 2 have the following relationship.

k1=2 (However, k is a value of 1 or more and is determined by the accuracy of evaluation.) The frequency divider 7 divides the clock pulse P1 of frequency 1 into 1/2 ⁿ , and divides the clock pulse P1 of frequency 1 into 1/2 n. Generate sampling pulse P3 for converter 2. Further, the pulse generator 8 divides or decodes the clock pulse P2 of frequency 2, and the multiplexer 4 divides or decodes the clock pulse P2.
Generate m control clock pulses necessary for time division multiplexing.

FIG. 2 shows an example of a specific circuit of the encoder circuit 3 and the multiplexer 4 when n=2 (bits).
It consists of a well-known 2line-to-4line decoder 31 and 2-input OR gates 32, 33, and 34, and
The multiplexer 4 is composed of a well-known 4 line-to-1 line multiplexer. In this case, the multiplexer 4 is supplied with two (m=2) control clock pulses having a frequency of 3 and 3/2 from the pulse generator 8.

FIG. 3 shows a 1-bit output waveform obtained by the circuit shown in FIG.

Below, c=4kHz, 1=2=3=4MHz (k=
The operation will be explained as 1).

The A/D converter 2 is supplied with a sampling pulse P3 of 1/2 ² of 4 MHz, that is, 1 MHz, from the frequency divider 7, and a 2-bit digital signal is outputted every 1 MHz.

Since this output is 2 bits, it takes one of the four values "11", "10", "01", and "00" as shown in FIG.

When the 2-bit value output from the A/D converter 2 is “11”, the corresponding output terminal of the decoder 31 is “11”.
A high (H) level signal is sent from the multiplexer 4, and the high level signal is input to all input terminals "3", "2", "1", and "0" of the multiplexer 4 by the OR gates 32, 33, and 34. .

Similarly, if the 2-bit value is "10", the decoder 3
A high level signal is sent from the output terminal "10" of the multiplexer 4, and the input terminals "2", "1",
A high level signal is input to “0”, and 2
When the bit value is "01", a high level signal is sent from the output terminal "01" of the decoder 31, a high level signal is input to the input terminals "2" and "1" of the multiplexer 4, and furthermore, When the 2-bit value is "00", a high level signal is sent from the output terminal "00" of the decoder 31, and a high level signal is input only to the input terminal "2" of the multiplexer 4.

On the other hand, since the multiplexer 4 receives 4MHz and 2MHz control clock pulses synchronized with the sampling pulse P3 of the A/D converter 2, the A/D converter 2 outputs a predetermined 2-bit value at a timing of 1MHz. While continues to be output,
Its input terminals "0", "1", "2", "3" are 4MHz
They will be selected sequentially at the following timings.

Therefore, if the 2-bit value is "11",
In each time slot of 4MHz, all the outputs are high level, and in the case of "10", the output is high level in the time slots "0", "1", and "2", and in the case of "01", the output is high level. "1",
It becomes a high level in the time slot of "2", and in the case of "00", it becomes a high level only in the time slot of "2", and as shown in Fig. 3, the value of 1 bit weighted on the time axis. Converted to waveform.

Furthermore, as in the above waveform, when the area of the waveform when the value of the 2-bit value is "00" is "α", "01" is "2α", "10" is "3α", "11" is a value proportional to a 2-bit numerical value, such as "4α".

Then, convert this 1-bit signal into an analog signal.
By passing the signal through the LPF 5, it can be restored to an analog signal with a band of 0 to 4 kHz, making it possible to evaluate and measure it with an analog measuring instrument.

(Effects of the Invention) As explained above, according to the present invention, a multi-bit digital signal, which is the output of an oversampling type A/D converter, is converted into a signal having a pulse width corresponding to the numerical value represented by the bit. and outputs this on the same signal line at regular time intervals.
Since it is converted into a bit binary signal and then converted into an analog signal by passing it through an analog filter, it is possible to use a digital filter for speed conversion and a multi-bit signal when evaluating and measuring using an analog measuring device. This eliminates the need to use a D/A converter, and has the advantage that the circuit for evaluation and measurement can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the method of the present invention;
FIG. 2 is a diagram showing an example of a specific circuit of an encoder circuit and a multiplexer, and FIG. 3 is a diagram showing an example of an output waveform. 1...Input terminal, 2...Oversampling type A/D converter, 3...Encoding circuit, 4...
Multiplexer, 5... Analog low-pass filter, 6... Clock generator, 7... Frequency divider, 8...
...Pulse generator, 9...Output terminal.

Claims (1)

[Scope of Claims] 1. A method for measuring AC characteristics of an oversampling type A/D converter in which an output digital signal of an oversampling type A/D converter with multiple bit output is converted into an analog signal and measured, comprising the steps of: The multi-bit digital signals outputted from the A/D converter at each sampling period are each decoded, each decoded output is made into a signal with a pulse width corresponding to its numerical value, and these signals are output at the same time interval at regular intervals. Output on the signal line to make a 1-bit binary signal, convert the 1-bit binary signal to an analog signal through an analog filter that passes only signals in the measurement band, and measure AC characteristics from the analog signal. An oversampling type A/D characterized by the following:
Method for measuring AC characteristics of converters.