JPS63111727A - Analog-digital converter - Google Patents

Abstract

PURPOSE:To apply A/D conversion to a broad band signal with a few comparators by varying a reference voltage given to a means subject to A/D conversion in response to an input signal level. CONSTITUTION:An analog signal inputted to an input terminal 10 is compared with each voltage division reference voltage formed by dividing a reference voltage at a reference input terminal 1 by resistors R1-R5 by comparators 17-21 and each comparison output is inputted to an encoder 22. The encoder 22 discriminates a level of an input analog signal by a comparison output signal from the comparators 17-21, and uses semiconductor switches 27-30 to select the minimum voltage among divided reference voltages larger than the level of the input analog signal voltage and gives the result to the 2nd stage 200 as a reference voltage. The 2nd stage 200 divides the reference voltage by resistors r1-rm, uses comparators c1-cm to compare each voltage with the input analog signal and inputs the result, of comparison to an encoder 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an analog/digital (^/D) converter, particularly an A/D converter in a video signal processing device.

[Conventional technology]

Conventionally, all-parallel type A/D converters for wideband signals such as video signals have often been used.

[Problem that the invention seeks to solve]

However, although high-speed conversion is possible with a fully parallel A/D converter, 2n-1 high-precision comparators must be used to configure an n-bit A/D converter. Therefore, devices with a large number of bits were expensive.

[Means for solving problems]

Human vision and hearing are not linear with respect to the level of input (light, sound); they have high resolution for low-level inputs, but the resolution decreases for high-level human inputs.

For example, in the case of vision, the detection limit for errors is said to be about 1% compared to human power.

Therefore, in consideration of the above, in the present invention, when A/D converting a video signal, the resolution of A/D conversion is made variable according to the signal level, thereby significantly reducing the number of comparators. The purpose is to realize a parallel type A/D converter and make it possible to reduce the size, power consumption, and cost of the A/D converter. /D conversion means, and means for changing the reference voltage applied to the means according to the input signal level.

[For production]

The present invention changes the reference voltage for A/D conversion according to the input signal level.

〔Example〕

FIG. 1 shows an embodiment of the invention. This embodiment is roughly divided into a first stage 100 that determines the resolution and a second stage 200 that performs ^/D conversion based on the resolution determined by the first stage 100.

As shown in FIG. 1, the analog signal (video signal) input to the input terminal 10 is connected to the reference voltage VRcr of the reference voltage input terminal 11 and the resistor R1 for determining the dynamic range.
, R2, R3, R4, and R5, and comparators 17, 18, 19, 20, and 2.
1 and each comparison output is input to the encoder 22. 23°24, 25. and 26 are buffer amplifiers that amplify each divided reference voltage. 2
7.28.29 and 30 are semiconductor switches,
Buffer amplifiers 23 to 26 are selected by selection signals to be described later.
One of them is selected and its output (divided reference voltage) is input to the second stage 200.

The encoder 22 determines the level of the input analog signal voltage based on the comparison output signals from each of the comparators 17 to 21,
27.28.29 The smallest of the divided reference voltages larger than the level of the human-powered analog signal voltage is selected by the semiconductor switch 27.28.29
．． By selectively selecting one of 30 and 30 using the selection signals 51 to S4, the reference voltage VRI! of the second stage 200! It is input to the same stage 200 as F'. The encoder 22 also inputs reference voltage level information to the encoder 30 of the second stage 200 using signals Bφ, Bl and OVF. The signal OVF sends information that an overflow has occurred, and the signal Bφ, 61 sends information as to which of the switches 27 to 30 is selected by the combination thereof.

The second stage 200 constitutes the same fully parallel A/D converter as the conventional one. That is, the reference voltage VREF' determined by the first stage 100 is divided and injected through a required number of resistors "1~rm," and each voltage is compared with the input analog signal using a required number of comparators c1~cm. , encoder 3
Input the comparison result in 0. In the encoder 30, the signals from each comparator and the signals from the first stage (OVF,
Bl, Bφ), determine the output value (digital voltage value corresponding to the human analog signal voltage),
The value is sent to the output terminal 1000.

According to the above, the resolution for the input analog signal can be switched in four stages. For example, in order to obtain a total dynamic range of 8 bits, a total of 69 comparators are required, and in order to obtain the same dynamic range, Compared to the conventional method, which required 255 comparators, this number is reduced, and a small, low-cost, high-speed A/D converter can be realized.

Note that in the above description, a case has been described in which the dynamic range is divided into four equal parts in the first stage 100, but this does not have to be four parts and may be divided into any number of parts. Further, there is no need to divide the image into equal parts, and the resolution switching point can be arbitrarily set using the resistors 81 to R5.

〔Effect of the invention〕

As explained above, according to the present invention, a wideband signal can be A/D converted with a small number of comparators.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. lO...Analog input terminal, 11...Reference voltage input terminal, 12-16...Reference voltage dividing resistor, 17-21.
c+ ~cm +++ voltage comparator, 23~26...
Buffer, 27-30... Analog switch, 22, 30... Encoder, r1-rm... Reference voltage dividing resistor, 1000...
Output terminal, 100...first stage, 200...second stage.

Claims (1)

[Claims] The invention is characterized by comprising means for comparing a reference voltage and an input signal and performing A/D conversion, and means for changing the reference voltage applied to the means according to the input signal level. A/D converter.