JP3155408B2 - D / A converter and test method for D / A converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a D / A converter,
And a D / A converter test method.

[0002]

FIG. 9 shows a conventional 4-bit parallel addition type D.
It is a block diagram of an / A converter. In FIG. 9, D
The / A converter 1 includes a decoder 3 and a plurality of analog signal sources 2 each of which can output a current of the same magnitude. BIT1 to BIT4 are digital signal input terminals, which are connected to the input section of the decoder 3, and the output section of the decoder 3
And the output of the analog signal source 2 is connected to OUT which is an analog signal output terminal.

FIG. 2 is a circuit diagram showing an example of the analog signal source 2 shown in FIG. In FIG. 2, the analog signal source 2 includes a switch 6 and a constant current source 7. The switch 6 is connected between the power supply and the constant current source 7 and turns on / off in response to a signal from the decoder 3.
In FIG. 2, when the signal from the decoder 3 is "1", the switch 6 is turned on, and when the signal from the decoder 3 is "0", the switch 6 is turned off. The constant current source 7 supplies a constant current to the output terminal OUT when the switch 6 is on.

FIG. 3 is a circuit diagram showing an example of the decoder 3 shown in FIG. In FIG. 3, the decoder 3 has an AN
It is composed of a D circuit, an OR circuit or a composite circuit thereof. The decoder 3 outputs a digital signal [B1 to B4]
To the digital input terminals BIT1 to BIT1 of the D / A converter 1.
The digital signal [A1 to A15] is input from the BIT 4 to the input of the decoder 3, and is output from the output of the decoder 3 to the input of the analog signal source 2.

[0005] Table 1 is a truth table of the decoder 3. The decoder 3 outputs the digital signal [B1 input to the digital input terminals BIT1 to BIT4 of the D / A converter 1.
To B4] are converted into digital signals [A1 to A15] for controlling the switch 6 inside the analog signal source 2 according to Table 1.

[0006]

[Table 1]

Next, D / D shown in FIG. 9, FIG. 2 and FIG.
The operation of the A converter 1 will be described. In FIG. 9, first, 4-bit digital signals [B1 to B4] are input to digital input terminals BIT1 to BIT4. The digital signals [B1 to B4] are input to the decoder 3, and according to the truth table of Table 1, the digital signals [A1 to A1]
5]. Next, the digital signal [A1 to A15] output from the decoder 3 is input to the analog signal source 2, and the switch 6 inside the analog signal source 2 is turned on or off depending on the state of the digital signal [A1 to A15]. I do. As a result, the sum of the outputs of the analog signal sources 2 in the ON state is output as an analog signal of the D / A converter 1 from the analog signal terminal OUT. The output analog signal is a 4-bit D / A
Since it is a converter, the signal has a 4-bit weight.

When measuring the analog signal of a 4-bit D / A converter with an accuracy of 0.1 LSB, assuming that the resolution at the time of measurement is εb, εb is

[0009]

(Equation 1)

## EQU1 ## That is, a measuring instrument having a resolution of 7.2 bits or more is required. In general, when measuring a D / A converter having a resolution of n bits with an accuracy of 0.1 LSB, the resolution of the measuring instrument needs to be (n + 3.2) bits or more.

[0011]

Since the conventional D / A converter is configured as described above, the n-bit D / A converter
When testing and evaluating the internal circuit of the A-converter (decoder, analog signal source, etc.) with an accuracy of 0.1 LSB,
A measuring instrument having a resolution of (n + 3.2) bits or more is required.

However, in recent years, the number of bits of a D / A converter has been increased, and therefore, in order to perform an internal circuit test and evaluation of a multi-bit D / A converter, a multi-bit D / A converter is required.
A measuring instrument having a high resolution that can support the A converter is required. However, there is a problem that a measuring instrument having a high resolution is generally very expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and eliminates the need for a measuring instrument having a high resolution when performing an internal circuit test and evaluation of a D / A converter, and at the same time, reduces the cost. / A that can reduce
The purpose is to obtain a converter, and D / A
The purpose is to provide a test method suitable for converters.

[0014]

According to the first aspect of the present invention, there is provided a digital camera comprising:
The / A converter includes an analog signal source, a first signal generation unit, a second signal generation unit, and a selection unit. The analog signal sources can generate analog signals each having the same weight.

[0015] The first signal generating means, data of the plurality of analog signal sources by decoding a digital input signal
Activate the analog signal source corresponding to the result of the code .

The second signal generator activates a plurality of analog signal sources individually. The selection means is connected to the first and second signal generation means, selects the output of the first signal generation means during normal operation, and generates the second signal when testing the internal circuit of the D / A converter. The output of the means is selected, and the output of the selected first or second signal generating means is provided to a plurality of analog signal sources.

A D / A converter according to a second aspect of the present invention includes a plurality of analog signal sources and a decoder. Each of the plurality of analog signal sources generates an analog signal having the same weight. Decoder means decodes a digital input signal to receive the signals from the plurality of analog signal sources.
Activates the analog signal source corresponding to the result of the last decoding
A first function to activate a plurality of analog signal sources individually, and a first function during normal operation, and a second function during an internal circuit test of the D / A converter. And a third function of selecting

A test of the D / A converter according to claim 3.
The method generates analog signals, each with the same weight
Includes multiple analog signal sources that can
Normal operation that outputs an analog signal corresponding to the
Operation mode and analog signals corresponding to each analog signal source
D / A converter having output internal circuit test mode
D / A converter test method for testing the operation of
A first step of selecting an internal circuit test mode;
In the internal circuit test mode, multiple analog signal sources
The second step which is activated separately, and the second step
Output value corresponding to each activated analog signal source
A third step of measuring
Corresponding to digital input signals in normal operation mode
Fourth step of evaluating the analog signal to be output
And a top. The D / A converter according to claim 4,
The test method is the test method of the D / A converter according to claim 3.
In addition to the construction of the method, the second step is
Receives different digital input signals sequentially and
A switch for generating a signal for sequentially activating the log signal source.
Including Tep. A test of the D / A converter according to claim 5.
Test method, the test method D / A converter according to claim 3, wherein
Fifth step for selecting the normal operation mode
And the digital input signal in normal operating mode.
The sixth step for outputting the corresponding analog signal is described below.
Be prepared.

[0019]

According to the first aspect of the present invention, during the normal operation, the first signal corresponding to the digital value of the digital input signal is selected to activate a plurality of analog signal sources. On the other hand, D /
When testing the internal circuit of the A-converter, a first signal for individually activating a plurality of analog signal sources is selected. By doing so, an analog signal can be output from the analog signal source alone, so that the D / A
The internal circuit test and evaluation of the D / A converter can be performed using a measuring instrument having a lower resolution than the measuring instrument having the resolution required for performing the internal circuit test and evaluation of the converter.

[0020]

FIG. 1 is an overall configuration diagram showing one embodiment of a D / A converter according to the present invention. The D / A converter shown in FIG. 1 is intended for a 4-bit parallel addition type D / A converter. Referring to FIG. 1, D / A converter 1 includes analog signal source 2 shown in FIG. 9, decoder 3 shown in FIG. 9, circuit 4 for individually operating analog signal sources, and selector 5. Have been. BIT1-BIT4
Is a digital signal input terminal, which is connected to each input section of the circuit 4 for individually operating the decoder 3 and the analog signal source, and each of the circuits 4 for individually operating the decoder 3 and the analog signal source. Is connected to the input of the selector 5, and the output of the selector 5 is connected to the input of each analog signal source 2, and the output of the analog signal source 2 is an analog signal output terminal. OUT. The selector 5 is connected to the control signal input terminal CONT.

FIG. 4 is a circuit diagram showing an example of a circuit 4 for individually operating the analog signal sources shown in FIG. The circuit 4 shown in FIG. 4 includes a plurality of AND circuits. The circuit 4 for individually operating the analog signal sources inputs the digital signals [B1 to B4] from the digital input terminals BIT1 to BIT4 to the input section of the circuit 4 for individually operating the analog signal sources, The digital signals [a1 to a15] are output from the output of the circuit 4 for individually operating the analog signal sources to the input of the selector 5.

Table 2 is a truth table of the circuit 4 for individually operating the analog signal sources. The circuit 4 for operating the analog signal sources individually converts the digital signals [B1 to B4] input to the digital input terminals BIT1 to BIT4 of the D / A converter 1 into selectors 5 according to Table 2.
Is converted into a digital signal [a1 to a15] to be input to the.

[0023]

[Table 2]

FIG. 5 shows an example of the selector 5. The circuit shown in FIG. 5 includes an AND circuit and a NOT circuit. In FIG. 5, the selector 5 receives digital signals [A1 to A1
15] and [a1 to a15] are input from respective outputs of the decoder 3 and the circuit 4 for individually operating the analog signal source to the input of the selector 5, and digital signals [A'1 to A'15] are inputted. From the output of the selector 5 to the input of the analog signal source 2. In FIG. 5, when "1" is input to the control signal input terminal CONT, the selector 5 converts the digital signals [A1 to A15] into digital signals [A'1 to A'15], When the control signal input terminal CONT is "0", the digital signals [a1 to a15] are output from the selector 5 as [A'1 to A'15].

Next, the D / A converter 1 of the first embodiment
Will be described. In FIG. 1, first, 4-bit digital signals [B1 to B4] are input to digital input terminals BIT1 to BIT4. Digital signal [B1
To B4] are input to a circuit 4 for individually operating the decoder 3 and the analog signal source. According to the truth tables of Tables 1 and 2, [A1 to A15] and [a1
To a15]. Next, the digitals [A1 to A15] and [a1 to a15] output from the circuit 4 for individually operating the decoder 3 and the analog signal source are input to the selector 5. The selector 5 converts the digital signals [A1 to A15] to [A ′] when “1” is being input to the control signal input terminal.
1 to A′15] and “0” is input to the control signal input terminal.
Is input, the digital signal [a1
To a15] as [A′1 to A′15]. The digital signal [A'1 to A '] output from the selector 5
15] is input to the analog signal source 2, and sets the switch 6 inside the analog signal source 2 to the on or off state according to the state of the digital signal [A1 to A15]. At this time, if “1” is being input to the control signal input terminal CONT, the sum of the analog signal sources 2 in the ON state becomes the analog signal of the D / A converter 1 and is output from the analog signal output terminal OUT. Is output. Since the output analog signal is a 4-bit D / A converter, it is a signal having a 4-bit weight. on the other hand,
If "0" is input to the control signal input terminal CONT, only one analog signal source 2 is in the ON state, and the analog signal output from the analog signal source 2 alone is the D / A converter 1 And is output from the analog signal output terminal OUT. The output analog signal is a signal having the weight of the analog signal source alone, and is a signal having a 1-bit weight in FIG.

Therefore, when measuring the analog signal of the 4-bit D / A converter shown in FIG. 1 with an accuracy of 0.1 LSB, if "1" is input to the control signal input terminal CONT, then 7. A measuring instrument having a resolution of 2 bits or more is required. On the other hand, if "0" is input to the control signal input terminal, a measuring instrument having a resolution of 4.2 bits or more is required. Therefore, even if the number of bits increases, measurement can be performed with a precision of 0.1 LSB using a measuring instrument having a resolution of at least 4.2 bits, and the cost required for the measuring instrument can be reduced.

Embodiment 2 FIG. 6 is an overall configuration diagram showing a second embodiment of the D / A converter according to the present invention.

The D / A converter shown in FIG. 6 is intended for a 3-bit parallel addition type D / A converter. Referring to FIG. 6, D / A converter 1 includes decoder 3 and FIG.
And the analog signal source 2 shown in FIG. B
IT1 to BIT3 are digital signal input terminals,
The output of the decoder 3 'is connected to the input of each analog signal source 2, and the output of the analog signal source 2 is connected to the analog signal output terminal OUT. I have. The decoder 3 'is connected to the control signal input terminal CONT.

FIG. 7 is a circuit diagram showing an example of the decoder 3 shown in FIG. The circuit shown in FIG. 7 is an AND circuit,
It is composed of an OR circuit or a composite circuit thereof.
6 and 7, the decoder 3 outputs the digital signal [B
1 to B4] are input from the digital input terminals BIT1 to BIT3 of the D / A converter 1 to the input section of the decoder 3 ', and digital signals [A1 to A7] are output to the analog signal source 2 from the output section of the decoder 3'. .

Table 3 is a truth table of the decoder 3 'in FIG. The decoder 3 'converts the digital signals [B1 to B3] input to the digital input terminals BIT1 to BIT3 of the D / A converter 1 into digital signals [A] for controlling the switch 6 inside the analog signal source 2 according to Table 1.
1 to A7].

[0031]

[Table 3]

The truth table of Table 3 is the same as that of Table 2 shown in Example 1.
Further, the truth table of Table 1 shown in the prior art is merely changed to a three-bit table. Therefore, as shown in FIG. 6, a function of operating the analog signal sources 2 having the same weight individually and a function of switching the internal circuit depending on the case of the internal circuit test and the normal operation of the D / A converter 1 are provided. To D
Even when the decoder 3 'which is a part of the internal circuit of the / A converter is provided, the same result as in the first embodiment can be obtained.

Embodiment 3 FIG. 8 is a flowchart showing a test method for a D / A converter.

This D / A converter test method has a function of individually operating analog signal sources having the same weight, and an internal circuit depending on whether the D / A converter is in the internal circuit test mode or in the normal operation mode. Using the switching function, D
This is a method for testing the A / A converter.

In FIG. 8, the circuit to be tested during normal operation operates in the order of step S1, step S2, step S3, step S4, step S5, and step S6. During normal operation, first, the control signal is set to "1" in step S2. Next, step S3
, An arbitrary digital signal is input to a digital input terminal. As a result, in step S4, an analog signal having a weight with respect to the sum of analog signal sources corresponding to the input signal is output from the analog output terminal.

[0036] In FIG 8, the circuit comprising a test of the subject at the time of testing an internal circuit, the step S1 → step S7 → step S8 → step S9 → step S10 → step S
11 operates in the order of step S12. At the time of the internal circuit test, the control signal is set to "0" in step S7. Next, in step S8, a digital signal pattern including a code from the least significant bit to the most significant bit is input to the digital input terminal. The digital signal pattern used at this time is determined according to the test conditions.
For example, in the case of performing a static linearity test, a digital signal pattern to be input is sequentially input one bit at a time from the least significant bit to the most significant bit. As a result, a plurality of analog signal sources inside the D / A converter are not turned on at the same time, and an analog signal having a single weight of the analog signal source corresponding to the input signal is output from the analog output terminal (step S1). S
9). For example, in the case of a parallel addition type D / A converter, a signal having a 1-bit weight is output.
The output analog signal is measured (step S10). Since the value obtained at this time is for each analog signal source, the output value for each code during normal operation is calculated from the measurement result (step S
11). For example, in the case of an n-bit parallel addition type D / A converter, the measured value (the output value of the analog signal source) is
[M (1) to M (2 ⁿ )] and the output value of each code [C
(1) to C (2 ⁿ )]

[0037]

(Equation 2)

## EQU4 ## Thus, the result of the internal circuit test of the D / A converter can be obtained by using the present invention.

[0039]

As described above, the D according to the first aspect of the present invention.
According to the / A converter, a second signal generating means for individually activating analog signal sources having the same weight is added,
By adding a selection means for switching the internal circuit depending on the case of the internal circuit test of the D / A converter and the case of normal operation, a resolution required for performing the internal circuit test and evaluation of the D / A converter is provided. The internal circuit test and evaluation of the D / A converter can be performed using a measuring device having a lower resolution than the measuring device. In general, the lower the resolution of a measuring instrument, the lower the cost. Therefore, the effect of reducing costs required for internal circuit testing and evaluation can be obtained.

Further, according to the D / A converter according to the second aspect of the present invention, the function of individually operating analog signal sources having the same weight can be obtained during the internal circuit test of the D / A converter and during normal operation. By providing the function of switching the internal circuit in each case, the internal configuration is simplified and the D / A converter is more simplified than the D / A converter according to the first aspect of the present invention.
The number of wirings between the internal circuits of the A converter can be reduced. Further, by adopting such a configuration, D /
The internal circuit test and evaluation of the D / A converter can be performed using a measuring instrument having a lower resolution than the measuring instrument having the resolution necessary for performing the internal circuit test and evaluation of the A converter. In general, the lower the resolution of a measuring instrument, the lower the cost, so that the effect of reducing the cost required for internal circuit testing and evaluation can be obtained.

According to the test method of the D / A converter according to the third aspect of the present invention, when performing the internal circuit test,
Since a plurality of analog signal sources can be individually activated, the output values of the activated individual analog signal sources can be measured, and the measured output values can be evaluated, so that the internal circuit test and evaluation of the D / A converter can be performed. The internal circuit test and evaluation of the D / A converter can be performed using a measuring instrument having a lower resolution than a measuring instrument having a resolution necessary for performing the above. In general, the lower the resolution of a measuring instrument, the lower the cost, so that the effect of reducing costs required for internal circuit testing and evaluation can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of a D / A converter according to the present invention.

FIG. 2 is a block diagram showing an example of the analog signal source shown in FIGS. 1 and 9;

FIG. 3 is a circuit diagram showing an example of the decoder shown in FIGS. 1 and 9;

FIG. 4 is a circuit diagram showing an example of a circuit 4 for individually operating the analog signal sources shown in FIG.

FIG. 5 is a circuit diagram illustrating an example of a selector illustrated in FIG. 1;

FIG. 6 is an overall configuration diagram showing a second embodiment of the D / A converter according to the present invention.

FIG. 7 is a circuit diagram illustrating an example of a decoder illustrated in FIG. 6;

FIG. 8 is a flowchart showing a test method of the D / A converter according to the present invention.

FIG. 9 is an overall configuration diagram of a conventional D / A converter.

[Explanation of symbols]

 Reference Signs List 1 D / A converter 2 Analog signal source 3, 3 'decoder 4 Circuit for individually operating analog signal sources 5 Selector 6 Switch 7 Constant current source

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-288616 (JP, A) JP-A-58-63227 (JP, A) JP-A-2-24984 (JP, A) JP-A 56-63 102120 (JP, A) JP-B 57-1169 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03M 1/00-1/88

Claims (5)

(57) [Claims] 1. A plurality of analog signal sources each generating an analog signal having the same weight, an analog signal source decoding a digital input signal and corresponding to a result of the decoding among the plurality of analog signal sources. First signal generating means for generating a first signal for activating the second signal source, second signal generating means for generating a second signal for individually activating the plurality of analog signal sources, and Connected to the first and second signal generating means, to select the output of the first signal generating means during a normal operation, and to select the output of the second signal generating means during an internal circuit test of the D / A converter; A D / A converter including a selection unit that supplies an output of the selected first or second signal generation unit to the plurality of analog signal sources. 2. A plurality of analog signal sources, each capable of generating an analog signal having the same weight, and a digital input signal , wherein the plurality of analog signal sources decode the digital input signal.
Analog corresponding to the result of the decoding of the signal source
A first function for activating a signal source, a second function for individually activating the plurality of analog signal sources, and the first function during a normal operation, and selecting the first function in the D / A converter. A D / A converter including a decoder having a third function of selecting a second function during a circuit test. 3. Each of the plurality of analog signal sources capable of generating the same weighted analog signal ,
Output analog signal corresponding to digital input signal
The normal operation mode and the analog corresponding to each of the analog signal sources
And an internal circuit test mode for outputting a log signal.
A D / A converter method for testing the operation of the A converter, a first step of selecting the internal circuit test mode, individually activating the plurality of analog signal sources in the internal circuit test mode first and second step, before SL on the basis of the third and steps, the output value the measurement for measuring an output value corresponding to each of the analog signal source is active activatable Te second step smell, the normal operation mode To
Output in response to the digital input signal.
D and a fourth step of evaluating can analog signal
/ A converter test method. 4. The method according to claim 1, wherein the second step includes a step of sequentially receiving digital input signals having different values from outside and generating a signal for sequentially activating the plurality of analog signal sources. 3. The test method of the D / A converter according to 3. 5. A fifth step for selecting the normal operation mode.
And digital input signals in the normal operation mode.
A sixth step of outputting an analog signal
The method for testing a D / A converter according to claim 3.