JPH0511446B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an A/D conversion circuit that converts an analog signal to a digital signal, and particularly relates to an A/D converter for television signals.

(Prior art) Conventionally, in the analog-to-digital conversion of television signals, the conversion speed is fast and the output bit count is high, so it is expensive. I was getting output. A block diagram and waveform diagram of an example of such a conventional A/D conversion circuit are shown in FIGS. 3 and 4a and 4b. The video signal supplied to the input terminal 1 is sent to A/D converters 4 and 5 via inverting amplifier circuits 2 and 3. The output digital data of the A/D converters 4 and 5 are combined by an arithmetic circuit 6 and output digital data is sent to an output terminal 7. The A/D converters 4 and 5 are supplied with a reference voltage from a reference voltage source 8, and the A/D converters 4 and 5 and the arithmetic circuit 6 are supplied with a clock from a clock pulse input terminal. The A/D converters 4 and 5 each divide between the ground potential and the reference voltage and set the input analog voltage to 0 in the case of 8 bits.
~255 data are output to the arithmetic circuit 6. The DC level regulator 9 adjusts the DC level of the input signals of the A/D converters 4 and 5, and outputs the input signals a' and b' (the third level) of the two A/D converters as shown in FIG. (see figure) is provided to shift the DC level by 2V.

(Problem to be Solved by the Invention) In the conventional A/D conversion circuit described above, the difference in the DC component between the signals a' and b' of the outputs of the inverting amplifier circuits 2 and 3 is such that the output data can be converted linearly. In order to change it, it is necessary to keep it within an error of several millivolts, but it has the disadvantage that it easily fluctuates due to changes in ambient temperature, power supply voltage, etc.

The present invention provides two A/Ds using feedback.
The present invention provides an A/D conversion circuit that can stabilize the relative DC level of an input signal to a converter.

(Means for solving the problem) According to the present invention, the first
a second amplifier circuit that inputs the analog signal, inverts and outputs the analog signal, first and second A/D converters that receive outputs from the first and second amplifier circuits, respectively; clamping means for clamping an analog signal output from a first amplifier circuit to a predetermined value and setting conversion ranges of the first and second A/D converters to different voltage ranges of the analog signal; an arithmetic circuit that combines the output data of the A/D converter and the inverted output data of the second A/D converter to obtain A/D converted data with an expanded number of bits;
and a reference voltage source that generates a reference voltage for setting the full scale of a second A/D converter; a differential amplifier circuit that extracts an offset error voltage for the first and second A/D converters from the difference with the reference voltage; and a feedback means that feeds back the output of the differential amplifier circuit to the first amplifier circuit. An A/D conversion circuit is obtained.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an A/D conversion circuit according to the present invention. The video signal supplied to the input terminal 11 passes through an inverting amplifier circuit 12 and a non-inverting amplifier circuit 13, and is sent to A/D converters 14 and 15, where it is A/D converted and output from the amplifier circuit 16 to an output terminal 17 as a digital signal. Data is sent.
The A/D converters 14 and 15 are supplied with a reference voltage (-2V) from a reference voltage source 18 for setting the full scale of A/D conversion. Inverting amplifier circuit 12,
The two signals from the non-inverting amplifier circuit 13 are mixed through a resistor of the same value, and the mixed output is supplied to the + side input of the differential amplifier circuit 21.
A reference voltage from a reference voltage source 18 is supplied to the - side input of the , and after amplifying the difference between the two inputs and attenuating high-frequency components, it is added to the DC voltage from the DC level adjuster 19. - of the non-inverting amplifier circuit 13
supplied to the side input. The DC level regulator 19 is used as a coarse regulator by supplying +4V as an offset voltage.

Assuming that the effective input range of A/D converters 14 and 15 is 0 to -2V, A/D converter 1
The waveforms of input signals a and b of 5 and 14 are shown in Figure 2 a and b.
The waveform will be as shown in . As shown in FIG. 2, the input signal b is the inverted version of the input signal a, and the DC level is higher than that of the input signal a from the reference voltage source 1.
The difference is twice (-4V) from the reference voltage of 8. Generally, the video signal pedestal shown in FIG. 2a is clamped to a constant voltage and used. Arithmetic circuit 16 inverts the signal from A/D converter 15 , adds it to the signal from A/D converter 14 , and outputs the result to output terminal 17 . In addition,
In the A/D converters 14 and 15, when the input signals b and a exceed the range of 0 to -2V, the output data is limited to 00...0, 11...1.

Further, the A/D converters 14, 15 and the arithmetic circuit 16 are supplied with a clock from a clock pulse input terminal 20. Furthermore, since the output signal of the differential amplifier circuit 21 is used to compensate for direct current fluctuations that are slower than the video signal, the output signal of the differential amplifier circuit 21 is a signal with the high frequency attenuated.

Amplification circuits that handle high-band signals such as video signals tend to be accompanied by DC drift, but in this example,
A low frequency differential amplifier circuit 21 compensates for the DC component. In the differential amplifier circuit 21 for low frequencies, one with less DC drift can be easily obtained.

The two A/D converters 14 and 15 use video signals b and a having different polarities and DC components, which are supplied from the two amplifier circuits 13 and 12. A/D
The DC level difference between converters 14 and 15 is
It is biased in order to accurately connect the effective range of A/D converter 14 and the effective range of A/D converter 15. When the input signals of the A/D converters 14 and 15 are added, the video signals a,
Since the polarity of b is reversed, there is only a DC component. The difference between this DC component and the reference voltage from the reference voltage source 18 is amplified and fed back to the amplifier circuit 13 to stabilize the DC level of the input signal to the A/D converter 14. The digital data from the two A/D converters 14 and 15 are combined in the arithmetic circuit 16 and sent to each A/D converter 14, 15.
Digital data with one bit more than the number of quantized bits of 15 is output.

(Effects of the Invention) As explained above, the A/D conversion circuit of the present invention feeds back the DC level of the video signal input to the two A/D conversion circuits via the differential amplifier circuit to which the reference voltage is input. This has the effect of improving the linearity of the output digital signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
Figures a and b are waveform diagrams of the signals a and b shown in Figure 1, respectively. Figure 3 is a block diagram of a conventional A/D conversion circuit. Figures 4 a and b are the signals shown in Figure 3, respectively.
It is a waveform diagram of a′ and b′. 1, 11... Input terminal, 2, 3, 12... Inverting amplifier circuit, 13... Non-inverting amplifier circuit, 4, 5, 1
4, 15... A/D converter, 6, 16... Arithmetic circuit, 7, 17... Output terminal, 8, 18... Reference voltage source, 9, 19... DC level regulator, 1
0, 20...Clock pulse input terminal.

Claims (1)

[Claims] 1 a first amplifier circuit that inputs an analog signal;
a second amplifier circuit that inputs, inverts and outputs the analog signal; and first and second A/Ds that receive outputs from the first and second amplifier circuits, respectively.
a converter, and clamps the analog signal outputted from the first amplifier circuit to a predetermined value.
and clamping means for setting a conversion range of a second A/D converter to a mutually different voltage range of the analog signal, output data of the first A/D converter and inverted output data of the second A/D converter. an arithmetic circuit that obtains A/D converted data with an expanded number of bits; a reference voltage source that generates a reference voltage for setting the full scale of the first and second A/D converters; and means for adding the outputs of the second amplifier circuit by resistor voltage division;
a differential amplifier circuit that extracts an offset error voltage for the first and second A/D converters from the difference between the resistor voltage division addition result and the reference voltage; An A/D conversion circuit comprising a feedback means for providing feedback to the circuit.