JPH1075160A - Automatic frequency controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce current, space and cost, while satisfying the severe specifications for a cellular telephone or the like by detecting the digital converted value of the DC voltage output of a discriminator, at the time of prescribed frequency reception and adjusting the oscillation frequency of a temperature compensated oscillator, so as to have the detected value match a reference value. SOLUTION: Reception signals from a base station are passed through a duplexer 1, amplified in an amplifier 2, lowered to a first intermediate frequency in a mixer 3, after passing through a filter 4, then lowered to a second intermediate frequency in the mixer 5, amplified and then frequency demodulated in the discriminator 8 and demodulated voice data are take out. A DC-voltage component outputted from the discriminator 8 is converted into a digital value by an A/D converter 13 and fetched to a CPU 14. Then, when an output value from the A/D converter 13 at a normal temperature and the reference value stored in a memory 15 are different, the CPU 14 outputs control signals to control the output of a temperature compensated digital crystal oscillator 12 and performs adjustment until both values match.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to FM (frequency modulation).
Frequency control (A
FC), and is a technique suitable for small mobile phones.

[0002]

2. Description of the Related Art For example, in an analog cellular telephone of a frequency modulation system, the deviation width of a transmission frequency is ± 1.0 ppm (1 ppm = 1 × 10 ^{−6) with} respect to a specified frequency f, and therefore, for a frequency f of 1 G Is 1 KH deviation is 1 KH
z (corresponding to z).

For this reason, since it is necessary to accurately respond to a received radio wave, a conventional analog cellular telephone uses, for example, a method of a radio block diagram shown in FIG. The circuit block includes a duplexer 21 for distributing a transmission wave and a reception wave, an amplifier 22 for amplifying a reception signal, a first mixer 23 for reducing the reception signal to a first intermediate frequency, a filter 24 for extracting only a difference between outputs of the mixer 23, a reception signal, 25, mixer 23 for lowering the frequency to the second intermediate frequency
A PLL frequency synthesizer 26 for producing a first intermediate frequency at P, and a P for producing a second intermediate frequency at mixer 25
LL frequency synthesizer 27, FM detector (discriminator) 28 for converting FM frequency to DC voltage, amplifier 29 for amplifying transmission wave to a specified level, mixer 3 for generating transmission wave by sum with output of PLL frequency synthesizer 26
0, a PLL circuit 31 for setting the frequency of the modulated wave to a transmission frequency in the mixer 30, synthesizers 26 and 27,
It comprises a temperature-compensated crystal oscillator 32 for outputting a reference frequency, such as a PLL circuit 31, and a PLL circuit 33 for adjusting the output of the oscillator 32 so as to accurately detect a predetermined FM frequency.

[0004] A received wave having a high-precision frequency arriving from a base station passes through a duplexer 21 and is transmitted to an amplifier 2.
After being amplified by 2 and dropped to the first intermediate frequency by the first mixer 23 and passed through the filter 24, it is dropped to the second intermediate frequency by the second mixer 25 and amplified,
FM demodulation is performed by the discriminator 28, and demodulated audio data is extracted. The discriminator 28 extracts a change in frequency with a DC voltage, and is known as a frequency discriminator.

A temperature-compensated crystal oscillator 32 uses an accurate reference frequency as a PLL frequency synthesizer 26 and a PLL.
By outputting to the circuit 31, an accurate transmission frequency can be generated and responded.

[0006]

However, the conventional circuit shown in FIG. 2 has a large number of components. Therefore, the standby current is large. It also increases costs.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides a PLL frequency synthesizer using the output of a temperature-compensated oscillator as a reference frequency, a frequency modulator for receiving the output of the PLL frequency synthesizer, A DC voltage output of the discriminator in an automatic frequency control apparatus including a mixer for mixing the frequency-modulated wave with the frequency-modulated wave and a discriminator for demodulating the frequency-modulated wave. An A / D converter for converting a digital value into a digital value; a storage means for storing an appropriate digital value to be output from the A / D converter as a reference value in advance when receiving the predetermined frequency; Control means for detecting the output value of the / D converter and adjusting the oscillation frequency of the temperature compensated oscillator so that the detected value matches the reference value Equipped with a.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG. FIG. 1A is a wireless block diagram of an analog cellular telephone showing a first embodiment of the present invention,
FIG. 1B is a wireless block diagram of an analog cellular telephone according to a second embodiment of the present invention.

In FIG. 1 (a), a received signal having a highly accurate frequency arriving from a base station is a duplexer 1.
, The signal is amplified by the amplifier 2, dropped to the first intermediate frequency by the first mixer 3, passed through the filter 4,
After being dropped to the second intermediate frequency by the second mixer 5 and amplified, it is FM-demodulated by the discriminator 8 to take out demodulated audio data. The DC voltage component output from the discriminator 8 is separately converted into a digital value by the A / D converter 13, and the digital value is taken into the CPU 14, which is the main control means of the telephone. The first local PLL frequency synthesizer 6 for generating the frequency to be mixed to produce the first intermediate frequency in the mixer 3 is conventional. The frequency to be mixed for producing the second intermediate frequency by the mixer 5 is generated by a fixed oscillator 7 of the second local. Transmission block amplifier 9, mixer 10, PL
The L circuit 11 is conventional. As an oscillator that outputs a reference frequency to the PLL frequency synthesizer 6 and the PLL circuit 11, a temperature-compensated digital crystal oscillator 12 having a higher accuracy of a temperature compensation function is used. The temperature compensated digital oscillator 12 accurately responds to the received signal by generating an accurate reference frequency, and generates an accurate transmission frequency.

By the way, the memory 15 sets an appropriate digital value to be output from the A / D converter 13 through the receiving block at the time of receiving an accurate predetermined frequency at an ordinary temperature at an ordinary temperature. It is stored as The frequency arriving from the base station has high accuracy. Therefore, the value output from the A / D converter 13 at room temperature is compared with the value stored in the memory 15, and when both values are different, both values are different. The CPU 14 may output a control signal for controlling the output of the temperature-compensated digital crystal oscillator 12 through the D / A converter 16 and adjust the signal until the values match.

The discriminator 8 has a temperature characteristic,
Because the DC voltage output varies with temperature,
Since the temperature characteristic of the second local oscillator 7 is also affected by the temperature characteristic, a certain temperature range width is set as a normal temperature, and the CPU 14 performs the automatic frequency control described above in principle. This is a time when it is confirmed that the temperature is normal temperature, for example, when the power is turned on, the above-described control is performed to the D / A converter 16 when the reference value matches the output value of the A / D converter 13. Is stored in the memory 15, and the control signal is continuously output until the power is turned off (the power switch is turned off). If the CPU 14 detects that the temperature is room temperature and the output of the A / D converter 13 does not match the reference value before the power is turned off, the above-mentioned automatic frequency is again adjusted so that both values match. Perform control again. Further, when the power is turned on, the CPU 14 performs the above-described control after confirming that various conditions such as a strong reception electric field strength (a predetermined level or more) and reception data are detected are satisfied in addition to the temperature confirmation. To

The automatic temperature control by the CPU 14 at normal temperature has been described above. When the temperature changes from normal temperature, the temperature-compensated digital crystal oscillator 12, whose output is corrected at normal temperature, operates in response to the temperature change. The frequency accuracy is maintained by the temperature compensation function of the oscillator 12 itself.

FIG. 1B is a radio block diagram of an analog cellular telephone according to a second embodiment of the present invention, and the same parts as those in FIG. In this example, the 2nd local fixed oscillator 7 in FIG. 7A is replaced with a PLL frequency synthesizer 7 'to provide higher accuracy, and the other parts are the same as those in FIG.

As described above, according to one embodiment of the present invention, an accurate transmission frequency can be generated by correcting the output of the temperature-compensated digital crystal oscillator 12 at normal temperature.

[0015]

As described above, according to the present invention, the number of PLL circuits conventionally required can be reduced, so that the current, space and cost can be greatly reduced. In addition, the accuracy is high because the automatic frequency control is performed on the arriving radio wave at room temperature, and the temperature change is realized by the performance of the temperature-compensated oscillator itself, so that the specified frequency deviation can be satisfied. That is, according to the present invention, it is possible to reduce current, space, and cost while satisfying strict specifications of a communication system such as a cellular phone.

[Brief description of the drawings]

FIG. 1 is a wireless block diagram of an analog cellular telephone according to an embodiment of the present invention, where (a) is the first embodiment,
(B) is a wireless block diagram of the second embodiment.

FIG. 2 is a wireless block diagram of an analog cellular telephone showing a conventional example.

[Explanation of symbols]

 1, 21: duplexer 2, 22: (receiver) amplifier 3, 23: 1st mixer 4, 24: filter 5, 25: 2nd mixer 6, 26: 1st local PLL frequency synthesizer 7: fixed oscillator 7 ', 27: 2nd b -Cal PLL frequency synthesizer 8, 28: FM detector (discriminator) 9, 29: (transmission) amplifier 10, 30: mixer 11, 31: PLL circuit 12, temperature-compensated digital crystal oscillator 13, A / D conversion 14: CPU 15: Memory 16: D / A converter 17: Temperature detecting means 32: Temperature compensated crystal oscillator 33: PLL circuit for automatic frequency control

Claims (1)

[Claims] A PLL frequency synthesizer using an output of a temperature-compensated oscillator as a reference frequency; a mixer for mixing an output of the PLL frequency synthesizer with a received frequency modulation wave to convert the frequency modulation wave into a frequency; An automatic frequency controller including a discriminator for demodulating the frequency-converted frequency-modulated wave, wherein the A / D converter converts a DC voltage output of the discriminator into a digital value.
A D converter, storage means for storing an appropriate digital value to be output from the A / D converter at the time of receiving the predetermined frequency as a reference value, and the A / D converter at the time of receiving the predetermined frequency.
An automatic frequency control device, comprising: control means for detecting an output value of the converter and adjusting an oscillation frequency of the temperature-compensated oscillator so that the detected value matches the reference value.