JPH0548659A - Fsk signal receiver - Google Patents

Abstract

PURPOSE:To make a local oscillating frequency of a 2-channel direct conversion system FSK signal receiver coincident with a reception frequency automatically. CONSTITUTION:An output of limiter amplifiers 11, 12 of a 2-channel direct conversion system FSK signal receiver and a system clock 16 of a decoder 17 are used to detect a difference of a frequency of an automatic frequency control section 18 and the result is fed back to a local oscillator 3 to make the oscillating frequency of a local oscillator coincident with a reception frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-channel direct conversion type FSK signal receiver for reducing the power consumption of an FSK signal receiver such as a pager.

[0002]

2. Description of the Related Art In order to reduce the size and power consumption of an FSK signal receiver such as a pager, a two-channel direct conversion FSK signal receiver (direct) is used.
A conversion receiver) has been proposed.

As a conventional example, FIG. 3 shows an example of a 2-channel direct conversion type FSK signal receiver.
The desired wave f _RF received by the antenna 1 is amplified by the high frequency amplifier 2. Local oscillation wave f generated by the local oscillator 3
_LOCAL is almost the same as the reception frequency, and is mixed in the mixer 5 in a phase equal to f _LOCAL and in the mixer 6 in a phase shifted by π / 2 by the phase shifter 4. The outputs from the two-channel mixers 5 and 6 generate a relative phase difference π / 2 due to the frequency shift of the received wave because of the phase shifter 4.
The high-pass filters 7 and 8 and the low-pass filters 9 and 10 respectively connected to the subsequent stages remove adjacent channel components and noise components to increase the S / N ratio, and the limiter amplifier 1
1 and 12 form a rectangular wave having a sufficient amplitude. Let ch1 and ch2 respectively.

Utilizing this relative phase difference π / 2, the discriminator 13 demodulates the transmission data. The discriminator 13 can be composed of a simple JK-FF or D-FF. Since the output of the discriminator 13 contains a high-frequency noise component, the low-pass filter 14 and the comparator 15 perform waveform shaping, and the decoder 17
Output demodulated data with. The decoder 17 operates on the system clock 16.

[0005]

As described above, in the conventional 2-channel direct conversion type FSK signal receiver, the local oscillator 3 is controlled by the bands of the high pass filters 7 and 8 and the low pass filters 9 and 10. The frequency offset is limited. In order to reduce the frequency offset, it is necessary to use a highly accurate crystal for the local oscillator 3, which leads to an increase in price. Further, if the band of the filter is widened, the receiving sensitivity tends to decrease.

The present invention solves such a problem, and an object thereof is to reduce the frequency offset without using a highly accurate crystal or the like.

[0007]

In order to solve the above problems, the present invention provides a two-channel direct conversion system F
The output of the limiter amplifier of the SK signal receiver is compared with the low frequency reference oscillation frequency, and the oscillation of the local oscillator is controlled by the difference between them to automatically oscillate the reception frequency and the frequency having no offset.

[0008]

The present invention has the following actions due to the above-mentioned configuration. That is, since it is not necessary to widen the filter band by automatically controlling the oscillation frequency of the local oscillator, the sensitivity can be increased, and since a crystal with high precision is not used, the price can be reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the present invention. 1 to 17 are the same as those in FIG. The present invention is characterized by adding the automatic frequency control unit 18. The automatic frequency control unit 18 includes limiter amplifiers 11 and 1
The frequency of the output of 2 is compared with the low frequency output obtained by dividing the system clock 16. In this case, it is better to compare the frequencies of the EX-OR of the outputs of the 2-channel limiter amplifiers 11 and 12 and the low frequency output obtained by dividing the system clock 16. The oscillation frequency of the local oscillator 3 is controlled by converting the frequency difference into a voltage, adding the voltage to the varicap of the local oscillator 3, and changing the capacitance thereof.

FIG. 2 shows a detailed configuration of the automatic frequency control section 18. Reference numeral 21 denotes an EX-OR unit, which is provided below the demodulated data (NRZ data) from the discriminator 13 and is provided with the limiter amplifier 1
The exclusive OR of 1 and the output of the limiter amplifier 12 is calculated and output to the counter unit 23. A timing edge output unit 22 divides the output of the system clock 16 at the output timing of the comparator 15 to create an edge of a timing signal (time t) equal to the data rate. 23
Is a counter unit, which counts the number of edges of the limiter amplifier output during the time t. A latch unit 24 latches the data counted by the counter unit 23. The latched data (number N) becomes f = N / t, the frequency difference is detected by the voltage control unit 25, the frequency offset is converted into a voltage offset, and the voltage offset is output. Change the capacity of. By changing the capacitance of the varicap, the local oscillator 3
The frequency of changes in the direction in which the offset from the reception frequency disappears and stabilizes at the frequency that matches the reception frequency. Since the stable data is stored in the memory 19, the convergence value hardly changes unless the reception frequency is offset.

[0011]

As is apparent from the above-described embodiment, the present invention eliminates the offset from the reception frequency without widening the band of the filter and without using a crystal with high precision in the local oscillator, and has a high sensitivity. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a 2-channel direct conversion FSK signal receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an automatic frequency controller unit in the embodiment.

FIG. 3 is a block diagram showing the configuration of a conventional 2-channel direct conversion FSK signal receiver.

[Explanation of symbols]

 1 Antenna 2 High Frequency Amplifier 3 Local Oscillator 4 Phase Shifter 5,6 Mixer 7,8 High Pass Filter 9,10 Low Pass Filter 11,12 Limiter Amplifier 13 Discriminator 14 Low Pass Filter 15 Comparator 16 System clock 17 Decoder 18 Automatic frequency controller 19 Memory 21 EX-OR block 22 Timing edge output section 23 Counter 24 Latch section 25 Voltage control section

Claims (1)

[Claims] 1. A receiving signal is demodulated by dividing a received signal into two and mixing each with a local oscillation wave having a relative phase difference and a relative phase difference between outputs of the mixing means. An FSK signal receiving apparatus having demodulation means and control means for controlling the oscillation frequency of a local oscillator based on the frequency difference between the output of the mixing means and the system clock of the demodulation means.