JPH04154319A - Encoder/decoder - Google Patents

Abstract

PURPOSE:To suppress the influence of noise generated in digital filters of a transmitting side and a receiving side by executing the connection after outputs of the digital filters of the transmitting side and the receiving side are stabilized. CONSTITUTION:While an output of a digital filter 2 is unstable, a gate circuit 3 is turned off, and when its output is stabilized, the gate circuit 3 is turned on and an output signal of the digital filter 2 is transmitted to an output circuit 11. When an output of a digital filter 12 is unstable, a switch circuit 14 opens a switch 15, turns on a switch 16 and sets an internal reference voltage of an output circuit 18. Also, when the output of the digital filter 12 is stabilized, the switch 16 is opened and the switch 15 is connected, and an output of a digital-to-analog converter 13 and the output circuit 18 are connected.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a code/decoder that performs mutual conversion between analog and digital signals, and particularly to a code/decoder that suppresses the influence of noise in digital filters. It is.

[Conventional technology]

In the conventional encoder/decoder, as shown in FIGS. 3(a) and 3(b), the transmitting side (FIG. 3(a)) receives an analog signal a.
A digital-to-analog converter (A/D) 30 that inputs in and outputs a digital signal dx+; a digital filter 31 that inputs a digital signal d0 and outputs a digital signal dxz; and digital signal d0. ．． Output circuit (S
, )32. Further, on the receiving side (FIG. 3B)), there is a digital filter (F33) which inputs the digital signal d in and outputs the digital signal d.

A digital signal that inputs the signal and outputs the analog signal al'l.
Analog converter (D/A) 34 and analog signal art
Input analog signal a. ,, an output circuit that outputs t (
St) 35. Normally, in encoders/decoders, in order to reduce power consumption, A/D
The converter, D/A converter, and digital filter are stopped to power down. Therefore, when the encoder/decoder is used, the power is increased to operate the A/D converter, D/A converter, and digital filter. At this time, it takes several m5ec until the output of the digital filters 31 and 33 becomes stable. During this time, noise as shown in FIG. 4 occurs in the outputs of the digital filters 31 and 33. Here, Tup is T when powering up.
+, Tz is the time for the output of the digital filter 31.33 to become stable. Therefore, the conventional encoder/decoder is directly affected by the noise of the digital filter, and the noise is output from the output of the output circuit.

[Problems to be Solved by the Invention] In this conventional encoder/decoder, noise is generated during power-up until the outputs of the digital filters on the transmitting side and the receiving side are stabilized. There was a drawback that noise was output.

SUMMARY OF THE INVENTION An object of the present invention is to provide an encoder/decoder that eliminates such drawbacks and suppresses the influence of digital filter noise even during power-up.

[Means to solve the problem]

The present invention provides an encoder/decoder that includes a digital filter that attenuates a specific frequency band on the transmitting side and the receiving side and performs mutual conversion between an analog signal and a digital signal. By providing a second switch circuit in the
The present invention is characterized in that the influence of noise caused by the digital filter is suppressed by turning off the first and second switch circuits.

Further, the encoder/decoder of the present invention includes: an analog/digital converter that converts an input analog signal into a digital signal; a digital filter that attenuates a specific frequency band from the digital signal; and a signal from the digital filter. The transmission side includes a gate circuit that connects and disconnects the digital filter, and an output circuit that outputs the signal from the gate circuit, and the gate circuit operates for a certain period of time until the operation of the digital filter stabilizes when the digital filter is powered up. When the digital filter and the output circuit are cut off and the output of the digital filter is stabilized, the digital filter and the output circuit are brought into a connected state to suppress the influence of noise from the digital filter.

Further, the encoder/decoder of the present invention includes: a digital filter that attenuates a specific frequency band from an input digital signal; a digital-to-analog converter that converts the digital signal from the digital filter into an analog signal; and an internal reference voltage. The receiving side includes a switch circuit that performs a switch operation, and an output circuit that outputs a signal from the switch circuit, and the switch circuit operates at a constant rate until the operation of the digital filter stabilizes when the digital filter is powered up. For a period of time, the internal reference voltage is connected to the output circuit and the connection between the digital-to-analog converter and the output circuit is cut off, and when the output of the digital filter becomes stable, the internal reference voltage and the output circuit are connected to each other. By cutting off the connection with the digital filter and connecting the digital-to-analog conversion circuit with the output circuit, the influence of noise from the digital filter is suppressed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, in which (a) shows the transmitting side and (b) shows the receiving side.

As shown in Fig. 1, this encoder/decoder includes an analog/digital converter (A/D) 1, a digital filter (F, ) 2, a gate circuit 3, and an output circuit ( S, ) 11, and the receiving side includes a digital filter (F, ) 12 and a digital-to-analog converter (D/
A) 13, switch circuit 14, and output circuit (32) 1
It is equipped with B.

The gate circuit 3 includes a NOT circuit 4, a NOR circuit 5, and an NOR circuit 5.
AND circuit 6 and MOS) transistor (P channel type)
9 and a MOS transistor (N-channel type) 10. The input terminal 4 is connected to a NOT circuit 5 and a NAND circuit 7.
is connected to the input. In addition, digital filter 2
The output of is connected to the NAND circuit 7 and the NOR circuit 6.

The output of the NOT circuit 5 is connected to the input of the NOR circuit 6,
The output of the NAND circuit 7 is connected to the gate of the MOS transistor 9, and the output of the NOR circuit 6 is connected to the gate of the MOS transistor 9.
) is connected to the gate of the transistor. The drain of the MOS transistor 8 is connected to the power supply side 8 (+■.Il), and the source is connected to the drain of the MOS transistor 10 and to one end of the output circuit 11.

Further, the source of the MOS transistor 10 is connected to ground. This gate circuit 3 is in an off state when the input terminal 4 is at a low level, and is in an on state when the input terminal 4 is at a high level. When in the on state, a signal from digital filter 2 is transmitted to output circuit 11 . While the output of digital filter 2 is unstable, gate circuit 3
is turned off, and when its output becomes stable, the gate circuit 3 is turned on and the output signal of the digital filter 2 is transmitted to the output circuit 11.

The switch circuit 14 consists of a switch 15, 16 and an internal reference voltage (ACM) 17. The output of the digital-to-analog converter 13 is connected to one end of the switch 15,
The other end of the switch 15 is connected to one end of the switch 16 and one end of the output circuit 18 . Further, the other end of the switch 16 is connected to an internal reference voltage (ACM) 17. When the output of the digital filter 12 is unstable (while generating noise), the switch circuit 14 opens the switch 15 and turns on the switch 16 to set the output circuit 18 to the internal reference voltage. When the output of the digital filter 12 becomes stable, the switch 16 is opened and the switch 15 is opened.
The output of the digital-to-analog converter 13 and the output circuit 18 are connected.

FIG. 2 is a signal waveform diagram showing the operation of this embodiment. Next, operations on the transmitting side and receiving side of this embodiment will be explained with reference to FIGS. 1 and 2.

First, the sending side will be explained. The analog signal atfi input to the analog-to-digital converter 1 is converted into a digital signal dxl, a specific frequency band is attenuated by the digital filter 2, and a signal dxt is output. At this time, when input terminal 4 is low, signal d, □
Regardless, MOS transistors 9 and 10 are turned off, and the output of gate circuit 3 is in a high impedance state. Further, when the input terminal 4 is high, the MOS transistors 9 and 10 are turned on, the output of the gate circuit 3 is turned on, and the signal dxt is input to the output circuit 11.

Therefore, as shown in FIG. 2, the input signal at the input terminal 4 is kept low (L) from the power-up of the encoder/decoder (Tup) until T when the output of the digital filter 2 becomes stable.
) and the signal from T1 is set high (H), the output circuit 11 is not affected by the noise of the digital filter 2 and can obtain a stable input signal.

Next, the receiving side will be explained. Digital filter 1
2, the digital signal d1. ．． , a specific frequency band is attenuated, a signal d, is output, and a digital signal is output.
It is converted into an analog signal ar+ by an analog converter 13. In the switch circuit 14, the digital filter 12
Switch 16 is turned on until the output of
), switch 15 is turned off (OFF) L, and after the output of the digital filter 12 is stabilized, switch 16 is turned off (OFF).
F), turning on the switch 15 (ON), therefore, the second
As shown in the figure, from Tup at power-up until Tz when the output of the digital filter 12 becomes stable, the switch 15 is turned off and the switch 16 is turned on, and the output circuit 18
The output of is connected to the internal reference voltage (ACM) 17. After the output of the digital filter 12 becomes stable, that is, T
By turning on the switch 16 from 2 and turning off the switch 15, and connecting the input of S2 to the output of the D/A converter, a stable input signal that is not affected by the noise of the digital filter 12 can be obtained.

〔Effect of the invention〕

As explained above, the present invention cuts off the output of the gate circuit while noise is generated in the output of the digital filter on the transmitting side, and shuts off the output of the gate circuit while the output of the digital filter on the receiving side generates noise. By connecting the output of the switch circuit to the internal reference voltage of the switch circuit and cutting off the output,
Since the outputs of the digital filters on the transmitting side and the receiving side are connected while being stable, it has the effect of suppressing the influence of noise generated in the digital filters on the transmitting side and the receiving side.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram in the embodiment of FIG. 1, FIG. 3 is a block diagram showing an example of the conventional technology, and FIG. This figure is a signal waveform diagram in the conventional example shown in FIG. 3. 1...Analog-digital converter 2.12...
・Digital filter 3...Gate circuit 13...Digital-to-analog converter 14...
...Switch circuit agent Patent attorney Yoshiyuki Iwasa (a) (b) Figure (a) (b) Figure 3

Claims (3)

[Claims] (1) In an encoder/decoder that is equipped with a digital filter that attenuates a specific frequency band on the transmitting side and the receiving side and performs mutual conversion between an analog signal and a digital signal, the first switch circuit is on the transmitting side and the first switch circuit is on the receiving side. By providing the second switch circuit, until the operation of the transmitter and receiver digital filters stabilizes at power-up,
An encoder/decoder characterized in that the influence of noise caused by the digital filter is suppressed by turning off the first and second switch circuits. (2) an analog-to-digital converter that converts an input analog signal into a digital signal; a digital filter that attenuates a specific frequency band from the digital signal; and a gate circuit that connects and cuts off the signal from the digital filter; An output circuit for outputting a signal from the gate circuit is provided on the transmitting side, and the gate circuit outputs the signal from the digital filter and the output circuit for a certain period of time until the operation of the digital filter becomes stable upon power-up. An encoder/decoder that suppresses the influence of noise from the digital filter by placing the digital filter in a cut-off state and, when the output of the digital filter becomes stable, connecting the digital filter and the output circuit. (3) It has a digital filter that attenuates a specific frequency band from the input digital signal, a digital-to-analog converter that converts the digital signal from this digital filter into an analog signal, and an internal reference voltage, and performs switch operation. A receiving side includes a switch circuit and an output circuit that outputs a signal from the switch circuit, and the switch circuit outputs the internal reference voltage for a certain period of time until the operation of the digital filter stabilizes upon power-up. is connected to the output circuit and the connection between the digital-to-analog converter and the output circuit is cut off, and when the output of the digital filter becomes stable, the connection between the internal reference voltage and the output circuit is cut off, An encoder/decoder that suppresses the influence of noise from the digital filter by connecting the digital-to-analog conversion circuit and the output circuit.