JPS5890844A - Analog-to-digital converter - Google Patents

Abstract

PURPOSE:To decrease the period of malfunction even with mixed error signals, by increasing the utilizing efficiency of encoded bit number and reducing the amount of data, through the differential pulse code modulation of a modulated wave signals angular-modulated with an analog signal. CONSTITUTION:An analog input signal ei is applied to a frequency modulator 10 for frequency modulation. A modulated wave signal eFM is applied to a low pass filter 11 in which high frequencies are attenuated in the rate of -6dB/oct, and an output e'FM is applied to a subtractor 2. An output eD=e'FM-e0 of the subtractor 2 is applied to an encoder 3 for encoding to obtain a digital signal ED. The digital signal ED is applied to a digital integrator consisting of an adder 4 and a latch 6 to generate an estimation signal E1. This estimation signal E1 is applied to a decoder 9 via a latch 8, where the signal is converted into an analog estimation signal e0 and applied to the subtractor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AD converter, which converts an analog signal into a digital signal by performing angle modulation such as frequency modulation and converting the angle modulated wave signal into a digital signal. To provide an AD converter which can reduce the amount of data to be obtained, has a short malfunction period due to noise contamination with a simple and inexpensive circuit, and can output correctly converted digital signals.

Conventionally, AD has been used to convert analog signals such as video signals into digital signals for supplying to memory for correcting time axis fluctuations in VTR playback signals, and for various other purposes.
A conversion device is used. In order to achieve high-efficiency encoding in such an AD converter, there has conventionally been a device that performs differential pulse code modulation (DPCM) as shown in FIG. In the figure, the analog signal ei input to the input terminal 1 is input to the subtracter 2.
Here, it is subtracted from the analog signal e0 of one clock before the decoder 9 and converted into a difference signal eDK, and then supplied to the encoder 3, where it is encoded by the 0 encoder 3. The extracted digital signal ED having the number of encoded bits n is supplied to the adder 4 and is output to the output terminal 5. The adder 4 adds this digital signal ED and the signal E, / obtained by dividing the addition output of the digital signal ED up to one clock ago by a predetermined coefficient by the divider 7, and produces the addition output signal. E0 is supplied to the latch 6 and latched. A signal E1 whose timing is aligned with the digital signal ED is taken out from the latch 6 and supplied to the divider 7, while a signal E1 whose timing is aligned with the digital signal ED is supplied to the latch 8.
is output. This signal ' is supplied to a decoder 9 and decoded into an analog signal. After that, subtractor 2
supplied to

In the above conventional device, the encoder 3. Decoder 9. Latch 6.8 Equal pressure supplied Figure 2 (B) and Figure 3 (6
), the input analog signal i has a frequency of 1 as shown in Figure 2 (4).
When it is a triangular wave of fc, the output signal 6p of the subtracter 2 becomes a trapezoidal wave as shown in FIG. 2DK. On the other hand, if the input analog signal e1 is a triangular wave with a frequency of 1 fC as shown in Figure 3, and the same amplitude as the nine triangular waves shown in Figure 2 (4), the output signal waveform of the subtracter 2 is A trapezoidal wave as shown in FIG. 3C) is formed, and its amplitude is V twice that of the trapezoidal wave shown in FIG. 2C).

In other words, if the number n of encoding bits is set so that the amplitude V of the trapezoidal wave shown in FIG.
The second triangular wave output from subtractor 2 when the triangular wave of
Figure C) The number of encoding bits for the trapezoidal wave shown by K is 2(n-
1'), and therefore the utilization efficiency becomes better as the frequency of the input analog signal e1 becomes higher. In other words, the utilization efficiency with respect to the number of encoded bits of the output signal of the subtracter 2 exhibits a characteristic of 5 d B 10 c t with respect to frequency.

Therefore, in the encoding of television signals that has already been made public, the apparatus shown in FIG. 1 has been used, taking advantage of the fact that the level value for the frequency of television signals is statistically -6 da10 ct.

However, when a television signal that is not based on the above-mentioned statistical prediction is received, the above-mentioned conventional apparatus cannot accurately convert the digital signal and obtain a correct reproduced signal e0. That is, the input analog signal 81 is a television signal as shown in FIG. , the difference signal eD obtained from the subtracter 2 is as shown in the same figure when focusing only on the signal part a)
The reproduced signal e is not an ideal waveform as shown in FIG. 1 but becomes a waveform as shown in FIG. The signal becomes K as shown in FIG. 0), resulting in a waveform significantly different from the original signal a.

In addition, in the conventional device described above, if an error occurs during operation, the error is added, so a means to periodically correct the error is required, and the circuit configuration is complicated. As mentioned above, the device has a utilization efficiency of 6dl1 for the number of encoded bits of the output signal of the subtracter 2 with respect to the frequency.
10ct, which had the disadvantage of poor utilization efficiency.

The present invention eliminates all of the above-mentioned drawbacks, and the fifth
One embodiment will be described with reference to the drawings below.

FIG. 5 shows a block system diagram of an embodiment of the AD conversion device according to the present invention. In the figure, the same components as those in FIG. The analog signal ei entering the input terminal 1 is supplied to the frequency modulator 10,
After being frequency-modulated and made into a frequency modulated wave signal 'FM, it is passed through a low-pass filter 11 with a frequency of -6dl110ct.
Frequency modulated wave signal e ′ that is attenuated by high frequency at a rate of
and is supplied to one input terminal of the subtractor M2.

FIG. 10 shows a circuit diagram of an embodiment of the low-pass filter 1. As shown in the figure, the low-pass filter 1 includes an NPN transistor Q whose pace is connected to the input terminal 12;
The collector resistance (resistance value R) and emitter resistance (resistance value R/) of the transistor Q, and the field effect transistor (F
ET) Q*, the base of transistor Q, and F E
A capacitor (
The amplified input signal is taken out from the collector of the transistor Q and supplied to the capacitor with the capacitance C, and the resulting voltage across the capacitor is converted into the FETQ that forms the source follower. , the impedance is converted and outputted to the output terminal 13. Now, the input voltage of the input terminal 12 is Vi.

When the output voltage taken out from the output terminal 13 is vo, the output voltage v0 is expressed by the following equation.

Vo ” Vi' (R・-) / (-1+R)
JωC ko'ωC = vl'/(j#C+Tt) 0, which is equivalent to passing through a low-pass filter of -15d110CL Therefore, the impedance of the capacitor j-
By setting C to a sufficiently large value compared to π, it is possible to configure the low-pass filter 11 with a simple R, C configuration.

Frequency modulated wave signal e extracted from the low-pass filter 11
, is converted into a digital signal ED by a circuit having substantially the same configuration as the AD converter shown in FIG. Note that the divider 7 shown in FIG. 1 is not particularly necessary and can be omitted because the signal supplied to the subtracter 2 is not a composite waveform of each frequency like a television signal, but a simple waveform. After frequency modulating the analog signal to be AD converted to obtain a frequency modulated wave signal "FM" with a constant amplitude, the signal is attenuated by -5 dB/Oct in advance and then supplied to the subtracter 2. Therefore, a difference signal eD whose level does not change even if the frequency changes can be obtained.
When the frequency of the output frequency modulated wave signal eFM' is 9, as shown in FIG. 6 (4), the difference signal eD extracted from the subtracter 2 is
The amplitude of is 5 d m with respect to the subtractor 20 input signal frequency.
/ o c t Therefore, in this embodiment, a frequency modulated wave signal eFM' having an amplitude of -6 da 10 at is supplied to the subtracter 2 according to the frequencies shown in FIG. 6 and FIG. 7 (4). The amplitude of the difference signal eD in the example case is as shown in Fig. 6.
As shown in FIG. 7C), both have the same amplitude V. Accordingly, according to this embodiment, the maximum number of encoding bits can always be used, so the utilization efficiency is greater than that of conventional devices.

WK, in the present invention, the signal to be converted into a digital signal is a frequency modulated wave signal "FM", so for example, the analog signal 6t is a television signal, and under normal conditions, the decoder 9 of the conventional device outputs the signal as shown in FIG. A normal television signal as shown in (4) is the reproduced signal e.

In this embodiment, as described above, the eighth
Of course, a frequency modulated wave signal with a normal waveform as shown in Figure @ is extracted from the decoder 9, but when a malfunction occurs, the reproduced signal e0 of the conventional device has an erroneous signal portion as shown in Figure 9 (4) k. While the television signal has a clipped portion C, in the case of a malfunction in this embodiment, the decoder 9
Frequency modulated wave signal e. As shown by the solid line in ) in the same figure, an erroneous signal portion b' and a clip portion C' occur, but the effect is on the frequency modulated wave signal e. Since it has a high frequency, it can be short. Incidentally, the frequency modulated wave signal e□.

The frequency band of e y M' + 60 is the frequency band of the current VTR.
When the device of the present invention is used as a part of the time base collector of , the frequency is about the same as the frequency modulation signal band of the current VTR, and the frequency is higher than the baseband of the signal. Further, the cutoff frequency of the low-pass filter 11 is selected, for example, to be approximately the lower limit frequency of the frequency modulated wave signal "FM" in the band including the -order sideband.

Note that the analog signal el converted into a digital signal by the device of the present invention is not limited to a television signal, but can of course be applied to audio signals and other analog signals. Further, a phase modulator may be used instead of the frequency modulator 10.

As described above, the AD converter according to the present invention includes an angle modulator that angle-modulates an analog signal, and attenuates the high frequency of the angle-modulated wave signal output from the angle modulator and supplies it to the differential pulse code modulation circuit. Since the present invention is equipped with a low-pass filter, the output reproduction signal of the decoder in the differential pulse code modulation circuit can be obtained accurately with a simple circuit configuration, instead of being based on statistical values as in conventional devices. In addition, since the amplitude of the differential signal can be kept almost constant regardless of changes in frequency, the efficiency of using the number of encoded bits can be greatly improved compared to the conventional method, and the amount of data when digitizing can be reduced. Even if an erroneous signal is mixed in, the period of malfunction is short, so malfunctions can be corrected in a short time.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram showing an example of a conventional device, Fig. 2 (A)-(Cri), Fig. 3 (■--), and Fig. 4 (4)-0.
are a signal waveform diagram for explaining the operation of FIG. 1, FIG. 5 is a block system diagram showing an embodiment of the device of the present invention, and FIGS.
FIG. 7 (A to 0 are signal waveform diagrams for explaining the operation of FIG. 5, respectively;
Figure 8 (B) and Figure 9 (@) are diagrams showing the reproduced signal waveforms in normal and malfunction conditions in Figures 1 and 5, respectively.
FIG. 0 is a circuit diagram showing an embodiment of the main part of FIG. 1... Φ analog signal input terminal, 2... subtractor, 3...
...Encoder, 4...-Adder, 5...Digital signal output terminal, 9...Decoder, 10-@Frequency modulator, 11...Low-pass filter 0 Fig. 3 Figure 4 (A) (B) (C)
(D) Figure 7 Figure 8 Figure 9 Figure 10■

Claims (1)

[Claims] An AD conversion device that converts an analog signal into a digital signal using a differential pulse code modulation circuit and outputs the digital signal, includes an angle modulator that angle-modulates the analog signal, and a high-frequency range of the angle-modulated wave signal output from the angle modulator. An AD conversion device comprising: a low-pass filter that attenuates a frequency and supplies it to the differential pulse code modulation circuit.