JPS6029027A - Signal converting circuit - Google Patents

Abstract

PURPOSE:To convert an analog signal into a digital signal of multi-adic code by applying code modulation to the analog signal to be converted into a PCM signal and D/A-converting the PCM signal into a digital signal with time compression. CONSTITUTION:An analog signal S0 inputted to an input terminal 11 is inputted to a sampling circuit 2. The circuit 2 and a coding circuit 3 constitute a pulse code modulating circuit, and after the circuit 2 samples the signal S0 at each prescribed Nyquist interval T1 to form a PAM signal S1, the circuit 2 outputs it to the circuit 3. Then the circuit 3 converts the signal S1 into a PCM signal S2 in m-bit and the signal is outputted to a D/A converter 5. The signal S2 is converted into a digital signal S3 having 2<n> stages of amplitude levels at each n-bit by the converter 5, the signal is fed to a magnetic head 6 as a digital signal in m/n-bit via a required modulation circuit and recorded on a magnetic tape 8. Further, a clock pulse CP inputted to a terminal I2 controls the timing of the circuits 2, 3, 5 respectively to compress the time axis and increase the recording density.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal conversion circuit that converts an analog signal into a multi-code digital signal.

In digital recording and playback, in which an analog input signal is digitized and recorded and played back on a recording medium, if the analog signal is converted into a digital signal in ternary or higher so-called multi-ary code and recorded on the recording medium, the occupied frequency can be reduced. This has the advantage of narrowing the band or improving recording density. However, circuits that encode sampled input signals into multi-ary codes have conventionally had the disadvantage of complex circuit configurations, and are generally
A binary pulse signal of °1" or °0", such as an M signal, has been used.

The present invention eliminates such conventional drawbacks and provides a signal conversion circuit that converts an analog signal into a multi-code digital signal by providing a simple additional circuit to a well-known pulse code modulation circuit. An example will be explained using drawings.

FIG. 1 is a block diagram of a recording system of a magnetic recording/reproducing apparatus to which the circuit of the present invention is applied, in which an analog signal S is input to a first input terminal 1. is input to the sampling circuit 2. The sampling circuit 2 receives an analog signal S. is the required Nyquist interval T
, by sampling each time to obtain a PAM signal S,
It is output to the encoding circuit 3.

The encoding circuit 3 converts this PAM signal S1 into m-bit PCM
It is converted into a signal S2 and output to the DA converter 5.

Here, the sampling circuit 2 and the encoding circuit 3 constitute a well-known pulse code modulation circuit 4.

The PCM signal S2 is converted to D every n times by the D=A converter 5.
-A conversion is converted into a digital signal S having an amplitude level of 2n steps, and is output to the magnetic head 6 via a required modulation circuit (not shown), so that the magnetic tape 8
recorded in

Frequency f of the clock pulse cp input to the second input terminal 12. is divided by the first counter 7 to obtain the sampling frequency f, thereby controlling the sampling timing of the sampling circuit 2, and is input to the encoding circuit 3 to be composed of m bits. The Nyquist interval (T, = 1/fl), which is the time length of one frame, is controlled. Further, the clock pulse cp is frequency-divided by the second counter 72 to have a frequency f2 (f, , = m f, ), and is input to the encoding circuit 3.
Pino 1-interval T2 of PCM signal S2 output from
T2 = l/f2).

Further, the clock pulse Cp is divided by the third counter 73 to have a frequency fs (f3=f2/n), so that the DA converter 5 has a via interval of T3 (T3
-1/f3), the PCM signal S2 is DA-converted every n bits to output a digital signal S3 of a multi-ary code.

FIG. 2 shows the output waveforms of each part when m = 4 and n-2, and (a) shows the analog signal S input to the input terminal 11. , (b) is the PA output from the sampling circuit 2
, M signal S, (C) is the 4-bit PCM signal S2 output from the encoding circuit 3, and (d) is the DA converter 5.
The digital signals S3 having two levels of amplitude levels outputted from the respective circuits are shown.

In the above-described circuit of the present invention, the circuit that converts the PCM signal into a multi-ary code is composed of a D-A converter, so when used in a recording/reproducing device, in a recording system that converts an analog signal into a digital signal, This makes it possible to replace the D-A converter that inputs a PCM signal and outputs a digital signal with 22 amplitude levels with a D-A converter that converts the PCM signal into an analog signal in the reproduction system. , it is possible to provide a multi-aryl encoding circuit with a simple circuit configuration and a narrow occupied frequency band.

In addition, the digital signal S3 is stored in a buffer memory (not shown).
By inputting data into the data, it is possible to compress the data on the time axis and improve the recording density. A digital signal having 22 amplitude levels at this time is shown in FIG. 2(e).

Note that in the circuit of the present invention, the m-bit PCM signal is
When performing 1)-A conversion for each bit, m/n is 2≦m/
Since any integer that satisfies the condition n < m is sufficient, the present invention is not limited to the above-mentioned embodiments, and, for example, by D-A converting a 15-bit PCM signal every 3 pins, an analog signal can be converted into 5-bit data. It is also possible to convert and record the amplitude level of each pulse into a digital signal with 23 levels, and it is not limited to magnetic recording media, but is a medium that can record signals corresponding to multiple amplitude levels. Of course, if there is, the present invention can be applied.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the present invention. 2... Sampling circuit, 3... Encoding circuit, 4... Pulse code modulation circuit, 5... D-A converter, 77.72.
73...Counter. Figure 2

Claims (2)

[Claims] (1) A pulse code modulation circuit that modulates an analog signal into an m-bit PCM signal, and a DA converter that performs D-A conversion on the PCM signal every n bits and outputs an m/n-bit digital signal. A signal conversion circuit characterized by comprising: (2) The signal conversion circuit according to claim 1, wherein the m/n is an integer satisfying a condition of 2≦m/n (m).