JPS6011494B2 - Analog/digital converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a feedback comparison type analog-to-digital converter.

An analog-to-digital (hereinafter referred to as A/D) converter using a feedback comparison method interposes a digital/analog (hereinafter referred to as D/A) conversion circuit between the output and one of the inputs of the bell comparator to apply feedback. The analog signal input to be converted into a digital signal and the output of the D/A converter are compared at the analog level, and when they match, the digital input to the D/A conversion circuit is set as the A conversion output. .

FIG. 3 schematically shows the main parts of this type of A/○ converter which uses a resistance ladder circuit for D/A conversion.

In the figure, numeral 31 is a well-known R-koi resistance ladder circuit, which consists of a resistor R and a resistor with twice the resistance value roughly combined in a ladder shape, and voltages of 10 V and -V are connected to the power terminal. A resistor r is added between the output terminal and the low voltage side power supply terminal to determine the slope of the output of the resistor ladder circuit 31.
is connected. The output LDS of the resistance ladder circuit 31 and the input of this A/D converter, that is, the analog signal ANL to be converted into a digital signal, are each output to a level comparator 3.
There are two non-inverting inputs and two inverting inputs. The analog switches 310, 311 for sequentially changing the output LDS of the resistance ladder circuit 31 are connected to a digital signal generating circuit 33 such as a microcomputer, for example.
The output LCS of the level comparator 32 is output to the digital signal generator 33 and the like. The operation of this circuit will be explained with reference to FIG.
11 Controls the on/off of...

Then, the output LDS of the resistor ladder circuit 31 increases the level, and the resistance values of the resistors r and R become (r) and (R), respectively.
Then, it reaches the maximum value of 5×2V, but during this time, the analog signal ANL generates a drumming bell.Then, the output LCS of the bell comparator 32 changes to high level, which causes the output of the digital signal generation circuit 33 at this time to However, when the difference between the two inputs of the level comparator 32 becomes close to the offset voltage, the output LCS will oscillate as shown in Fig. 4, and change to the level /. There is a problem that the timing cannot be determined safely and accurate A/D conversion output cannot be obtained.To solve this problem, the output of the level comparator 32 is received by a flip-flop, and the set output of this flip-flop is converted into a digital signal. The present invention enables accurate A/D without adding circuit components such as flip-flops.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing embodiments thereof, with the object of providing an A/D converter that can stably obtain a conversion output.

FIG. 1 schematically shows the external part of an A/D converter according to the invention.

1 is an R-order resistance ladder circuit, which consists of a resistor R and a resistor 2R having twice the resistance value, arranged in a ladder shape.
Voltages of 10V and -V are applied to the two power supply terminals, respectively.

The output LDS of this resistance ladder circuit 1 is used as the non-inverting input of the bell comparator 2, and the input of this A/D converter,
That is, the analog signal ANL to be converted into a digital signal is used as the inverting input of the bell comparator 2. The same voltages as the power terminals of the resistance ladder circuit 1, 10 V and 1 V, are applied to the positive and negative power terminals of the level comparator 2, respectively. Furthermore, in the A/D converter of the present invention, a resistor r is connected between the output terminal of the resistor ladder circuit 1 and the output terminal of the level comparator 2. As will be shown later, this resistor r functions as a resistor that determines the strength of the output of the resistor ladder circuit 1, and also functions as a feedback resistor. Note that the relative relationships among the values of the resistors R, 2R, and r are the same as in the conventional circuit shown in FIG. And output LCS of level comparator 2
is output to the digital signal generating circuit 3, etc., and the output of the digital signal generating circuit 3 turns on/off the analog switches 】0, 11... of the resistor ladder circuit 1. It is similar to the circuit. Next, the operation of this circuit will be explained based on FIG. The analog switch 1 of the resistor ladder circuit 1 is activated by the binary code generated by the digital signal generating circuit 3 while increasing its value sequentially.
0, 11......... are turned on in a predetermined order.
OFF, and during this time the output LDS of the resistor ladder circuit 1 becomes the second
It continues to rise as shown in the figure. Then this output LDS
is lower than the analog input ANL, the output LCS of the level comparator is at a low level, that is, at the level of 1 V, so the resistor r is connected to the low voltage side power supply terminal to which 1 V of the resistor ladder circuit 1 is applied. It functions as a resistor that determines the value of the output of the resistor ladder circuit 1. Therefore, the output LDS of the resistance ladder circuit 1 exceeds the analog input ANL, or the difference between the two becomes close to the offset voltage of the level comparator 2,
Once the output LCS of the level comparator 2 becomes a high level, its output terminal is connected to the output terminal of the resistor ladder circuit 1 via the resistor r, and this high level is a level of 10 V, so the resistor ladder Since the output LDS of the circuit 1 is pulled up to the positive side, it becomes definitely larger than the analog input ANL by that amount, and the output LDS of the level comparator 2 does not fall to the low level but remains at the high level. Such a zero level comparator output LCS is used as a signal for extracting the output content of the digital signal generation circuit 3 as an A/D conversion output when it changes to the /. This makes it possible to stably obtain accurate A/D conversion output. In this way, the A/D of the present invention
While configuring the output voltage range of the converter ladder comparator 2 to match the power supply voltage of the resistor ladder circuit 1,
Since the output terminal of this resistance ladder circuit and the output terminal of the bell comparator are connected through an appropriate resistor that also serves as a resistor for determining the slope of the output of the resistance ladder circuit, no special parts are required. , and accurate A
The present invention has excellent effects such as being able to perform /D conversion stably.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the main parts of an A/D converter according to the present invention, FIG. 2 is an explanatory diagram of its operation, and FIG. 3 is a circuit diagram showing the main parts of a conventional A/D converter. FIG. 4 is an explanatory diagram of its operation. 1...Resistance ladder circuit, 2...Level controller, 3...Digital signal generation circuit. Traditional 1 drawing, 2 drawings, 4 drawings, 3 drawings

Claims (1)

[Claims] 1. A feedback comparison type analog/digital converter equipped with a resistance ladder circuit for digital/analog conversion and configured to input the output signal of the resistance ladder circuit and the analog signal to be converted to a level comparator, The output voltage range of the level comparator is configured to match the power supply voltage of the resistor ladder circuit, and the output terminal of the resistor ladder circuit and the output terminal of the level comparator are connected via an appropriate resistor. analog/digital converter.