JPH04208719A - A/d converter - Google Patents

Abstract

PURPOSE:To make a device inexpensive and small sized by combining an A/D conversion part having the (M-N)-bit resolution, an A/D conversion part having the N-bit resolution, and a D/A conversion part. CONSTITUTION:An output signal S1 of a second A/D conversion part 3 is sent as a binary code corresponding to a decimal in accordance with the magnitude of the output signal of a sampling and holding circuit 1. The output of a D/A conversion part 4 to which the output signal S1 is inputted is supplied as an analog voltage to a reference input terminal 6 of a first A/D conversion part 2. The second A/D conversion part 3 subjects the output of the sampling and holding circuit 1 to A/D conversion at a high speed with a low resolution. An output signal S2 of the second A/D conversion part 3 is joined with the output of the first A/D conversion part 2, and binary input data from the first A/D conversion part 2 is left shifted in a digital data converting circuit 5 by K bits.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A/D converter, and more particularly to an A/D converter that secures the number of effective bits when a low level input signal is received by using an A/D converter with a small resolution. [0002]

2. Description of the Related Art Conventionally, this type of A/D converter is disclosed in Japanese Unexamined Patent Publication No. 1-212921. [00031 FIG. 3 is a block diagram of an A/D converter showing an example of such a conventional converter. [0004] As shown in FIG. 3, a conventional A/D converter includes a sampling and holding circuit 1 that temporarily stores an input analog signal from an analog input terminal IN, and a signal input to this sampling and holding circuit 1. a level detector 10 that detects the level of
MAN: A to convert into a digital signal of both natural WL)
It has a /D conversion section 11 and a signal processor 12 which inputs the converted digital signal and the output of the level detector 10 and performs signal processing. The signal processor 12 that performs this signal processing shifts the N-bit digital signal to the right and converts it to (N+K) bits (M-N≧K).
The digital signal is outputted to the digital data output terminal OUT. [0005] With this A/D converter, the effective number of bits of the converted output can be ensured even when the input analog signal is at a low level, compared to the case where the input analog signal is simply input to the A/D converter and A/D converted. can do. [0006]

[Problem to be solved by the invention] The above-mentioned conventional A/D
The converter requires an analog amplifier that accurately changes the amplification depending on the input level of the input analog signal. Furthermore, when such an analog amplifier is used in a high-resolution A/D converter, it has the disadvantage that it is difficult to integrate into an integrated circuit due to its large size. [0007] It is an object of the present invention to provide an A/D converter that can be made inexpensive, compact, and easily integrated into an integrated circuit without using such a precise analog amplifier. [0008]

[Means for Solving the Problems] The A/D converter of the present invention inputs an analog signal, converts it into M (M is a natural number) bits of digital data, and samples the analog signal. resolution (M-N) (N is smaller than M), which is equipped with a sampling and holding circuit for holding and a reference input terminal for determining the range of input signals to be A/D converted, and inputting the output of the sampling and holding circuit; a first A/D converter of [Natural number] bits, a second A/D converter of N bits of resolution that receives the output of the sampling and holding circuit as input, and an output of the second A/D converter. and a digital data conversion circuit that synthesizes the output of the first A/D converter and the output of the second A/D converter, the D/A converter is configured to create an input signal for the reference input terminal based on the output of the unit. [0009]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. [00101 FIG. 1 shows an A/D showing a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a converter. [00111 As shown in FIG. 1, this embodiment includes a sampling and holding circuit 1 that inputs an analog signal, temporarily samples and holds it, and an input signal range for A/D conversion, where M and N are natural numbers. A first A/D converter 2 having a reference input terminal 6 to determine and inputting the output of the sampling and holding circuit 1 with a resolution of (M-N) bits; an N-bit second A/D converter 3;
A D/A converter 4 which inputs the output of the second A/D converter 3 and returns it to an analog signal and supplies it to the reference input terminal 6.
and a digital data conversion circuit 5 that bit-shifts the output of the first A/D converter 2 based on the magnitude of the output of the second A/D converter 3 and outputs the result. [0012] First, the input analog signal input to the analog input terminal IN is input to the sampling and holding circuit 1, and the output of the sampling and holding circuit 1 is sent to the first A/D converter with a resolution of (M−N) bits. 2 and a second A/D converter 3 with a resolution of N bits. Here, M and N are natural numbers with a relationship of M>H. Further, the output signal S1 of the second A/D converter 3 is 2K from 1 to 211 (where K≦N-1, is an integer greater than or equal to 0) depending on the magnitude of the output signal of the sampling and holding circuit 1. ) is sent in a binary code corresponding to a decimal number. D/ that inputs this output signal S1
The output of the A converter 4 is applied to the reference input terminal 6 of the first A/D converter 2 at an analog voltage V1×2 (V
+ is the minimum reference voltage). That is, the input range of the first A/D converter 2 is the reference input terminal 6.
is determined by the analog voltage VIX2 applied to VIX2. On the other hand, the second A/D converter 3 performs A/D conversion of the output of the sampling and holding circuit 1 at high speed with low resolution. The output signal S2 of the second A/D converter 3 is a signal for shifting the binary input data from the first A/D converter 2 to the left by a bit. This operation is performed in the digital data conversion circuit 5 together with the output of the D conversion section 2. As a result, the digital data conversion circuit 5 outputs M-pit binary data to the output terminal OUT. [0013] In short, an A/D with a resolution of M−N bits
By combining the converter 1, the N-bit A/D converter 3, and the D/A converter 4, there is no need to use a high-precision analog amplifier to directly amplify the input signal, and the N-bit A/D converter 3 is combined with the D/A converter 4. Valid bits, ie (M−N) bits, can be secured in the level range. [0014] FIG. 2 shows an A/D according to a second embodiment of the present invention.
FIG. 2 is a configuration diagram of a converter. [00151 As shown in FIG. 2, this embodiment is an example in which an input signal touches the positive and negative sides of the ground level, such as an audio signal.Compared with the first embodiment described above, They are the same except that the reference terminals 6A and 6B of the first A/D converter 2 and the means for supplying analog signals thereto are different. The details will be explained below. [0016] The analog input bone is sampled and held in a sampling holding circuit 1, and the output signal of this sampling holding circuit 1 is sent to a first A/D converter 2 and a second A/D converter 3. added to. The output of the first A/D converter 2 is input to the digital data converter 5, and the output of the second A/D converter 3
The first output S1 is input to the D/A converter 4. [0017] The output of this D/A converter 4 is sent to the absolute value circuit 7
to create the absolute value of the analog signal. The output of the absolute value circuit 7 is input to the positive side reference input terminal 6A of the first A/D converter 2, and the amplification degree is -
The signal is inputted to the negative side reference input terminal 6B of the first A/D converter 2 via the 1x amplifier 8. In short, the first A/D converter 2 is an A/D converter whose input range is the voltage range given to the two reference input terminals 6A, 6B. On the other hand, the second A/
The output signal S2 of the D converter 3 is input to the digital data converter circuit 5, which converts the output signal of the first A/D converter 2 into the second A/D converter 3. This circuit shifts the signal to the left according to the magnitude of the output signal S2. In this way, the A/D converter of this embodiment can handle low-resolution A/D even when the input signal swings to both the positive and negative sides.
/D converter can be used to perform high-speed conversion. That is, the effective bits for small signals can be increased. Therefore, when used for A/D conversion of audio signals, etc., the dynamic range can be expanded. [0018]

As explained above, the A/D converter of the present invention combines two A/D converters with lower resolution when converting an analog signal into a digital signal, and converts one A/D converter into a digital signal. By changing the reference voltage or reference current of the other A/D converter depending on the magnitude of the analog input signal input to the other A/D converter, the effective number of bits can be maintained when the input signal is at a low level. . Furthermore, by using a low-bit A/D conversion section, the present invention eliminates the need for an amplifier that accurately variable amplifies the analog input signal, making it inexpensive and compact, making it suitable for integrated circuits, and This has the effect of achieving high resolution.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an A/D converter showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an A/D converter showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an A/D converter showing a conventional example.

[Figure 1]

[Figure 2]

[Figure 3]

Claims (2)

[Claims] Claim 1: Input an analog signal to M (M is a natural number)
The A/D converter converts and outputs bit digital data, and includes a sampling and holding circuit that samples and holds the analog signal, and a reference input terminal that determines an input signal range to be A/D converted. A first A/D converter with a resolution (M-N) [N is a natural number smaller than M] bits that takes the output of the holding circuit as input, and a second A/D converter with N bits of resolution that takes the output of the sampling and holding circuit as input. a D/A converter that receives the output of the second A/D converter as input, and a D/A converter that receives the output of the first A/D converter and the second A/D converter; An A/D converter comprising: a digital data conversion circuit for synthesizing outputs of the converting section, and creating an input signal for the reference input terminal based on the output of the D/A converting section. 2. The A/D converter according to claim 1, wherein the digital data conversion circuit is constructed using a shift register.