JPS5933944A - Circuit for preventing quantized noise - Google Patents

Abstract

PURPOSE:To prevent the quantized noise at non-signal with a simple circuit constitution, by interrupting the transmission of signal when the range of a PCM signal value is quantized and clocks are counted for a prescribed number. CONSTITUTION:When an amplitude of an input sound signal is small, a PCM signal is quantized at a quantizing circuit 5, an output Q of a count circuit 7 goes to logical value ''1'' and a transmission control circuit 4 stops the transmission of the PCM signal, then the circuit is constituted so as not to produced the quantized noise. Even if a pulse noise is generated at non-signal and this noise is quantized at a quantizing circuit 6, the counter circuit 7 is not initialized unless the duration time exceeds >=3 period's share of the clock, and the circuit 4 keeps stopping the transmission of the PCM signal.

Description

[Detailed description of the invention] Is the input sound estrus sign not yet invented? Analog to digital conversion (
The present invention relates to a quantization noise prevention circuit for a circuit that digitally processes a PCM signal subjected to AD (hereinafter referred to as AD).

An AD circuit is used to time sample the input acoustic signal and convert it into a pcu signal. The AD circuit converts the amplitude of the input audio # signal into a digital signal.If the conversion bit is N, the amplitude of the input audio signal is quantized in a 2N quantization area, and the corresponding digital signal is The signal is converted into a number of PCM signals. The quantization unit is A (unit;
volt), the maximum amplitude of the input acoustic signal needs to be A.2. FIG. 1 is a time chart showing an example of the operation of the AD circuit when the amplitude of the input acoustic signal is small.

In Figure 1, horizontal lines (al, (bl, (c)
It shows the threshold value of the quantization area of the A D circuit. Therefore, the period between (a) and (bl and between (b) and (01) is the η conversion unit A described by luI. tel indicates the input acoustic signal waveform. T1 to T4 are the sampling points of ADI 1st pass. ((1) shows the conversion output of the lowest focus of the AD rotation U combination.

Now, as is clear from FIG. 1, minute fluctuations in the input acoustic signal near the quantization area become quantization noise in the AD circuit. Even a slight noise variation in fFtl, no signal 11#, becomes a quantization noise variation corresponding to the lowest bit variation of the AD circuit. In order to eliminate this noise fluctuation, the AC bias point of the input acoustic signal must be '! m (a) and (
The KM quantization threshold may be set in the middle of b) or between (b) and (C), but the interval A of the quantization threshold is the maximum amplitude T of the input acoustic signal.Generally N is 8-12
Therefore, A is a minute amount, and it is difficult to keep it stable in the middle of the quantization threshold due to temperature changes, changes over time, etc.

Pulse noise has a short duration, but a relatively wide amplitude, and if sampled by chance, it also becomes one of the noise fluctuations. When the human acoustic signal is changing, the minute noise is not audible due to the masking effect, but
Micronoise when there is no signal is extremely annoying to the ears9.

What has not yet been invented is a circuit means for preventing the occurrence of such quantization noise in the case of non-operation, and will be explained in detail below with reference to the drawings.

In FIG. 2, (1) is the audio signal input terminal, (2) is the first clock input terminal, and (3) is the AD[! -! l road, (
4) is the transmission side (goods) circuit, (5) and (6) are the first and second mouse conversion circuits, (7) is the first counting circuit, (8) is the shift register, (9) is the AND It is a gate.

AD circuit T#J (31 time-samples the input sound tube signal 'fr exclusively for the input terminal IN, every first clock applied to the CK terminal, and converts it into an N-bit PCM signal.

This N-bit pcu signal is transmitted to each input terminal (DI to D) of the first quantization circuit (5) and the second quantization circuit (6)
N) K, etc., the value range Ml of the PCM signal is quantized. The range in which the value of the PCM signal, which is composed of digital codes (signal) and (ADI to ΔDN), changes is small;
The output of the quantization circuit (5) becomes logic ``1''. If the amplitude of the human acoustic signal is greater than or equal to pJ1 quantification, and the value of the PC\ signal is greater than or equal to the predetermined value!, then the second quantum conversion circuit (6
) becomes logic ``1''. The first counting circuit (7) outputs the first quantization circuit (7) only when the output of the first quantization circuit (5) becomes logic ``1''. Count the ri...ri. When a predetermined number of first chronographs are counted, the output Q of the first argument circuit (7) becomes logic "1" and the counting function is stopped. A shift register (8) samples and shifts the output of the second quantization circuit (6) using the first clock. Therefore, when the output of the second quantization circuit (6) is logic 1'1" during the 6 cycles of the first clock, the outputs of the shift register (8) Ql+Q2+Q, qu all become logic "1", and As a result, the output of the AND gate (9) becomes logic "1", and the output of the first counting circuit (7) is initialized.

The transmission control circuit (4) transmits the PCM signal applied to the input spores (D1 to DN) to the output terminals (PI to PN) K when the output Q of the first counting circuit (7) is logic "0". , argument f”
When i''', it is configured to output a constant digital value.The transmission circuit (4) may also be configured as a latch circuit, and when the OT large input logic is O° The latch operation is performed every cycle of the first clock, and the launch operation is not performed when the OT large input logic is tT I I+, so that the output does not change.

With the above configuration, when there is no signal and when Rlj, the amplitude 1 of the input acoustic signal, is small, the PCM signal is quantized by the first quantization circuit +51 K, and the output Q of the first counting circuit (7) is When υ is logic "1", both transmission side circuits (4) stop transmitting the PCM signal, so it is possible to have a configuration that does not generate quantization noise. Of course, pulse-like noise occurs when there is no signal, and this must be equal to or more than 6 cycles of the second quantum rx
The first counting circuit (7) is not initialized, and therefore the output control circuit (4) is at the point where it stops transmitting the PCM signal.

Incidentally, even if the output of the first quantization circuit (5) is logically inverted instead of the output of the second @ childization circuit (6), the above explanation and Mr. rri's VC7! function. Further, the initial value of the first counting circuit is determined by the output of the second quantizing circuit (6) or the inversion of the output of the first quantizing circuit (5) at the constant timing of the first clock. You may have it performed when it reaches 1"K. In this case, pulse-like noise at the time of no signal becomes quantization noise, but steady quantization noise can be prevented.

As described above, according to the quantization noise prevention circuit of the present invention, quantization noise can be prevented when there is no signal with a simple circuit configuration.

[Brief explanation of the drawing]

Figure 1 shows the analog signal when the amplitude of the input acoustic signal is small.
A time chart diagram showing an example of the operation of a digital conversion circuit,
FIG. 2 is a block circuit diagram of the quantization noise prevention circuit of the present invention. (1)...Acoustic signal input terminal, (2)...First clock input terminal, (3)...Analog-digital conversion circuit,
(4)...transmission control circuit, (5)...first quantization circuit,
(6)...Second quantization circuit, (7)...First counting circuit, (8)...Shift register, (9)...Second counting circuit.

Claims (1)

[Claims] +1+(a) An analog signal that time-samples the input acoustic signal using the first clock and converts it into a PCM signal.
a digital conversion circuit; (b) first and second elementization circuits that quantize a range of values of the PCM signal into which the input acoustic signal is converted; (cl) based on the output of the rabbit conversion circuit; a first counting circuit that counts a first clock (or a clock corresponding to this); (a) a shift that samples and shifts the output of the second generator circuit using the first clock (or a clock corresponding to this); (e) the analog register;
and a transmission sterilization circuit that transmits the PCM signal output from the digital conversion circuit to the subsequent digital processing circuit, and the first counting circuit is initialized by the @ period shift register output, and the transmission sterilization circuit The circuit controls the transmission of the PCM signal by the output of the first counting circuit, and when the amplitude of the input acoustic signal is small (referred to as no-signal time), the value range of the PCM signal is within the first Ail period. When the first counting circuit counts the first clock to a predetermined value, Af
The circuit interrupts the transmission of the PCM signal of the output of the A ”lν
The value range of one signal is quantized by the second quantization path (=f) and stored in the shift register based on one clock G, and the first counting circuit is initialized based on the second quantization circuit. , the Mfl notation system 611 circuit is M 'j',
A circuit for preventing quantization noise when there is no signal, which is characterized by transmitting a PCM signal to a subsequent digital processing circuit (C) (2) Second quantization] Step 1 is to perform quantization in the first quantization circuit. 2. The quantization noise prevention circuit when there is no signal according to claim 1, wherein the PCM signal value range other than the value range is quantized. (3) The quantization noise prevention circuit at the time of no signal as set forth in claim (1) or (2), wherein the first counting circuit is initialized by the output of the second quantization circuit. (4) The transmission side diagonal circuit is characterized in that whether to transmit the PCM No. 9 to the subsequent digital processing circuit or to transmit a predetermined digital value is controlled by the output of the first counting circuit. Claims (1), (2) or (3)
Monthly noise prevention when there is no signal described in K rJ = circuit 0