JP2964580B2 - Encoder for PB received signal - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an analog / digital encoder for PB (push-button dial) reception signals, and more particularly to a PB reception signal code used in a subscriber circuit of a digital exchange. About the vessel.

[Prior Art] Conventionally, as an encoder for a PB reception signal, for example, in an audio signal PCM codec, after an analog bandpass (channel) filter for blocking other than the audio band of an analog signal, an A / D Transformer provided, quantized A
There is one that encodes the output of the / D converter,
As shown in FIG. 4, there is a configuration in which a channel filter 3 realized by a digital filter using digital signal processing is provided after the A / D converter 2.

In this digital filter codec, A / D
A pre-filter 1 composed of a low-pass filter is provided in front of the converter 2 so that an analog input signal having a frequency equal to or less than 1/2 of the A / D sampling frequency is input to the A / D converter 2. . The analog signal that has passed through the pre-filter 1 is input to the A / D converter 2, and the digitally converted signal is passed through a channel filter 3 composed of a high-pass filter 4 and a low-pass filter 5 so that only the necessary band is obtained. Signal is taken out.

[Problems to be Solved by the Invention] Usually, the overload level of the A / D converter is the maximum amplitude value of the AC signal input with the DC offset 'zero', and the analog signal is small and the DC offset is superimposed. Even if it is within the input range of the A / D converter, the DC offset is removed by the low-pass filter 5 of the channel filter 3.

However, when the encoder is connected to the output of the 2-wire to 4-wire conversion circuit of the subscriber circuit, when the subscriber presses the push button, the telephone transmits the PB signal and the DC resistance changes at the same time. DC is transiently superimposed on the PB signal. For this reason, there is a disadvantage that the input range of the A / D converter is exceeded and as a result, the PB signal cannot be passed.

Also, if a certain amount of DC offset voltage is allowed,
There was a problem that the accuracy of the A / D converter could not be used effectively.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a PB reception signal encoder that reduces non-passage of a PB signal.

[Means for Solving the Problems] To achieve the above object, a PB received signal encoder according to the present invention includes an A / D converter for digitizing an analog signal related to a PB received signal.
A channel filter including a D converter, a digital filter for extracting only a necessary band of the A / D converted digital signal, and an overload detection unit for detecting that an output of the A / D converter is overloaded. And a ground circuit for grounding an analog signal input terminal to an A / D converter to a reference potential with low impedance when the overload detection unit detects the overload.

Then, if necessary, a pre-filter for limiting a signal to a band equal to or lower than 1/2 of the A / D sampling frequency is provided at the front of the A / D converter.

[Operation] According to the PB received signal encoder having the above configuration, the A / D
If the output of the converter is overloaded, the overload detector detects this and the detection activates the grounding circuit, thereby reducing the DC level.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a PB received signal encoder according to one embodiment of the present invention.

In the figure, reference numeral 1 denotes a pre-filter, and this pre-filter 1 converts an analog signal for a PB reception signal input to an A / D converter 2 at the next stage to an A / D sampling frequency of 1
/ 2 or less. The A / D converter 2 digitizes this analog signal. The A / D converter 2 is connected to a channel filter 3 for extracting only a necessary band of the A / D converted digital signal. The channel filter 3 includes a high-pass filter 4 and a low-pass filter 5.

Further, the encoder includes an overflow detector 6 serving as an overload detection unit for detecting that the output of the A / D converter 2 is overloaded. When the overflow detector 6 detects an overload, And a ground circuit 7 for grounding the analog signal input terminal to the / D converter 2 with a low impedance to a reference potential. The ground circuit 7 is configured using, for example, CMOS-SW using ON resistance.

As shown in FIG. 2, the encoder for a PB reception signal according to the embodiment is connected to, for example, an output of a high-pass filter for AC detection of a subscriber circuit (LC) 8. A telephone 9 for a push-button dial signal is connected to the subscriber circuit 8.

Therefore, telephone 9 connected to this subscriber circuit 8
When the user presses the push button, the telephone 9 changes the DC resistance and transmits a PB signal. The transmitted PB signal is input to the encoder through the high-pass filter in the subscriber circuit 8. In the encoder, the pre-filter 1 sets the analog signal input to the next-stage A / D converter 2 to a half or less of the A / D sampling frequency. The signal is output through a high-pass filter 4 and a low-pass filter 5 of a channel filter 3 connected to the output of the A / D converter 2. In this state, the output of the A / D converter 2 is detected by the overflow detector 6 as an overload of the A / D.

In this state, if the signal input to the A / D converter 2 has a transient waveform in which a DC component is superimposed, the DC change causes the signal to exceed the A / D overload level, and the A / D converter 2 The output code of 2 overflows. For this reason, the overflow detector 6 detects the overflow, thereby driving the low-impedance grounding circuit 7 and lowering the time constant of the high-pass filter to lower the DC level.

That is, as shown in FIG. 3, the conventional A / D input waveform A exceeds the overload level and the output non-passing time T1 is extended, but according to the embodiment, the A / D input waveform Since B is reduced below the overload level, the output non-passing time T2 is shortened.

[Effects of the Invention] As described above, according to the encoder for a PB reception signal of the present invention, when a PB signal is received, a transient signal on which a DC is superimposed is generated.
Detects that the output of the A / D converter is overloaded, grounds the input terminal with low impedance, reduces the time constant of the filter, and quickly returns the input voltage of the A / D converter from the overload level Therefore, there is an effect that the non-passing time of the PB signal can be shortened while sufficiently using the accuracy of the A / D converter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a PB received signal encoder according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a use state of the encoder according to the embodiment, and FIG. Graph showing the input waveform and output waveform of the encoder in comparison with the conventional,
FIG. 4 is a block diagram showing an example of a conventional PB received signal encoder. 1: Pre-filter 2: A / D converter 3: Channel filter (band-pass filter) 4: High-pass filter 5: Low-pass filter 6: Overflow detector 7: Ground circuit

Claims (2)

(57) [Claims] An A / D converter for digitizing an analog signal related to a PB reception signal, a channel filter including a digital filter for extracting only a necessary band of the A / D converted digital signal, and an A / D converter An overload detection unit that detects that the output of the converter is overloaded, and when the overload detection unit detects the overload, the analog signal input terminal to the A / D converter is set to the reference potential with low impedance. An encoder for a PB reception signal, comprising: a ground circuit for grounding. 2. A PB according to claim 1, further comprising a pre-filter for limiting a signal to a band equal to or less than 1/2 of an A / D sampling frequency, in front of said A / D converter. Encoder for received signal.