JPH0766741A - Ific for pager - Google Patents

Abstract

PURPOSE:To reduce the degradation of receiving sensitivity due to noise by providing this pager IFIC with a comparator haying hysteresis for converting an analog waveform outputted from a low pass filter(LPF) into a digital waveform. CONSTITUTION:The pager IFIC is constituted of an FM detector 32, an LPF 34 and a comparator 36 having hysteresis. The comparator 36 having hysteresis is constituted of a comparator having hysteresis, a resistor, a capacitor, and a quick charging part. When the hysteresis of the comparator 36 is set up to 1/3 of a maximum input level, the comparator 36 output a high level signal when an input level is >=2/3 of the maximum input level and outputs a low level signal for the input level <=1/3 of the maximum input level. Consequently a 10dB down point from the LPF 34 can be set up to an equivalent noise band, so that no noise waveform is outputted from the comparator 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pager IFIC.
Regarding the improvement of.

[0002]

2. Description of the Related Art Miniaturization of pagers has become a major issue, and for this reason, it has been promoted to integrate each main part into an IC for each block. The IF amplifier is integrated into a single chip. In such an IFIC, the audio unit has the configuration shown in FIG. That is, it is composed of an FM detector 2, a low-pass filter (LPF) 4, and a comparator 6.

The FM detector 2 is usually of the quadrature type, the LPF 4 is of the second or third order, or a combination thereof, and the comparator 6 is a simple comparator without hysteresis.

FIG. 2 shows a specific circuit of the LPF 4 and the comparator 6. The LPF 4 includes resistors 8, 10, 12 and capacitors 14, 16, 18 and a comparator 20, and the comparator 6 includes a comparator 22 and a capacitor 24.
And a quick charge unit 26.

[0005]

A in the circuit of FIG.
Waveforms at points b, c are shown in FIGS. 3 (a), (b), (c).
Shown in.

If the fundamental wave which is the input of the LPF 4 shown in FIG. 3A has a large level of noise at a high frequency close to the fundamental wave as shown by 30, the LPF 4 attenuates the noise (see FIG. ) Waveform 30 ') and noise 30' are generated by the comparator 2
If it is larger than the threshold value of 2, noise of the same level as the fundamental wave is output to the output of the comparator 6 as indicated by 30 ″ in FIG. Becomes

That is, in the case where the LPF is of the third order or fourth order, the cutoff frequency of the LPF and the cutoff frequency of the comparator output are deviated, and the equivalent noise band is widened. As a result, Receiving sensitivity is reduced.

An object of the present invention is to provide an IFIC for pager which solves such a problem.

[0009]

SUMMARY OF THE INVENTION The present invention is based on the idea that the comparator should have hysteresis so that the noise waveform 30 'shown in FIG. 3 (b) is not sensed.

The pager IFIC of the present invention comprises an FM detector, a low-pass filter for low-pass filtering the signal detected by the FM detector, and an analog waveform output from the low-pass filter, which is converted into a digital waveform. And a comparator having hysteresis.

[0011]

FIG. 4 shows the structure of an IFIC for pager of the present invention. This pager IFIC is based on the FM detector 3
2, LPF 34, and comparator 36 having hysteresis.

FIG. 5 shows a specific circuit of the LPF 34 and the comparator 36 having hysteresis. LPF34
Is the same as the LPF 4 in FIG. Therefore, its components are shown with the same reference numerals as in FIG. The comparator 36 having hysteresis includes a comparator 38 having hysteresis, resistors 40 and 42, a capacitor 44, and a quick charge unit 46.

As an example, if the hysteresis of the comparator 36 is set to 1/3 of the maximum input level V _MAX as shown in FIG. 6, the comparator 36 outputs "3/2" or more of the maximum input level. "High" is output, and "Low" is output for an input level of 1/3 or less of the maximum input level.

As a result, the point of 10 dB down of the LPF 34 can be set as the equivalent noise band. Therefore, since the noise waveform 30 'of FIG. 3 (b) is not sensed,
The comparator 36 does not output the noise waveform 30 ″ of FIG.

Although the comparator 36 is input to the digital circuit of the next stage, noise is removed, so that no malfunction occurs.

[0016]

The IFIC which does not adopt the configuration of the present invention has a band of about 25 to 30 dB down, but according to the present invention, for example, in the case of a third-order LPF, about 1 octave,
It became possible to narrow the band. Therefore, it is possible to reduce the deterioration of the reception sensitivity due to noise.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an audio unit of a conventional IFIC.

FIG. 2 is a diagram showing a specific circuit of the LPF and the comparator of FIG.

3 is a waveform diagram in the circuit of FIG.

FIG. 4 is a diagram showing a configuration of an IFIC for pager of the present invention.

5 is a diagram showing a specific circuit of the LPF and the comparator of FIG.

6 is a diagram showing input / output characteristics of the comparator of FIG.

[Description of Reference Signs] 32 FM Detector 34 LPF 36 Comparator with Hysteresis

Claims (1)

[Claims] 1. An FM detector, a low-pass filter for low-pass filtering a signal detected by the FM detector, and a comparator having hysteresis for converting an analog waveform output from the low-pass filter into a digital waveform. An IFIC for a pager, which is provided.