JPH11355102A - Afc side lock preventing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the side lock of AFC even when the precision of TCXO (temp. compensation-type crystal oscillator) is deteriorated in the AFC control of a mobile body communication system which is represented by a PDC(personal digital cellular) system digital portable telephone. SOLUTION: An AFC side lock preventing circuit is provided with a TCXO 10 to be an original vibration of an RF part and a voltage control oscillator(VCO), the RF part 11 of for converting a signal received from an antenna down to an IF band, the VCO 12 for generating an IF×N clock, a frequency difference detecting part 13 for detecting a frequency difference from an IF signal, a frequency correcting part 14 for correcting a frequency from a frequency correction pulse and outputting an after correction IF signal (AFCIF), an AFCIF counter 15 for counting the AFCIF signal for a fixed period, an IF counter 18 for counting the IF signal for a fixed period and a CPU 16 for controlling a D/A converter 17 which varies a voltage to TCXO 10 by the measurement results of the AFCIF counter 15 and the IF counter 18. Thus, the side lock of AFC is prevented even when TCXO 10 is deteriorated in precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an AFC control circuit of a mobile communication system typified by a (personal digital cellular) type digital cellular phone, and is particularly configured to prevent side lock during AFC control.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of a conventional AFC control circuit. In FIG. 3, a conventional AFC control circuit includes a temperature-compensated crystal oscillator (TCXO) 30 serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), and an RF for down-converting a signal received from an antenna to an IF band. Department
31, a voltage controlled oscillator (VCO) 32 for generating an IF × N clock, a frequency error detection unit 33 for detecting a frequency error from the IF signal, and a corrected IF signal (AFCIF ), An AFCIF counter 35 for counting the AFCIF signal for a certain period, and a D / A converter for varying the voltage to the TCXO 30 based on the measurement result of the AFCIF counter 35.
And a CPU 36 for controlling the 37.

Next, the operation of the conventional AFC control circuit will be described with reference to FIGS. In FIG. 3, RF
The frequency error detection unit 33 detects and accumulates the leading and lagging of the frequency from the IF signal output from the unit 31, and outputs a frequency correction pulse. The frequency correction unit 34 normally divides the IF × N clock generated by the voltage controlled oscillator (VCO) 32 by N. However, the frequency correction pulse from the frequency error detection unit 33 divides the frequency by N−1 and N + 1. The circuit goes around to generate an AFCIF signal.

[0004] The AFCIF counter 35 has an AFC
The frequency of the IF signal is measured, and the CPU 36 reads the value of the AFCIF counter 35. The CPU 36 calculates a correction value from the read value, writes a value for controlling the frequency of the temperature-compensated crystal oscillator (TCXO) 30 in the D / A converter 37, and performs AFC control.

AFC control is performed during reception (at the time of continuous reception and synchronization acquisition). Further, in the conventional configuration, a high-precision temperature-compensated crystal oscillator (TCXO) 30 is used, so that the frequency does not deviate to a position that greatly exceeds the quadrant that should originally exist in FIG.

[0006]

However, when considering the use of a temperature-compensated crystal oscillator (TCXO) with inferior accuracy in the above-described conventional circuit configuration, the electric field sensitivity is deteriorated and the IF in a wrong quadrant is considered. When the signal is demodulated and out of synchronization occurs, if the frequency of the IF signal (TCXO) is shifted to the vicinity of the center of the wrong quadrant, the frequency error is not detected by the frequency error detection unit, and the frequency is used as AFC control. The AFC side lock state locks to the wrong value.

The present invention solves the above-mentioned conventional problems. A temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), and a signal received from an antenna is converted to an IF band. An RF unit that downconverts the signal to a voltage-controlled oscillator (V
CO), a frequency error detection unit for detecting a frequency error from the IF signal, a frequency correction unit for performing frequency correction from the frequency correction pulse and outputting a corrected IF signal (AFCIF), and an AFCI for counting the AFCIF signal for a certain period of time.
An F counter, an IF counter for counting an IF signal for a certain period, and a CPU for controlling a D / A converter for varying a voltage to the TCXO based on the measurement results of the AFCIF counter and the IF counter. However, an object of the present invention is to provide a circuit that prevents side lock during AFC control.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), and a signal received from an antenna. An RF unit for down-converting to the IF band, a voltage controlled oscillator (VCO) for generating an IF × N clock, a frequency error detecting unit for detecting a frequency error from the IF signal, and correcting the frequency from the frequency correction pulse. A frequency correction unit that outputs a corrected IF signal (AFCIF), and an A that counts the AFCIF signal for a certain period.
FCIF counter; IF counter for counting IF signals for a certain period; AFCIF counter and D / A for varying voltage to TCXO based on measurement results of IF counter
A CPU for controlling the converter is provided. Even if the accuracy of the TCXO is degraded, the IF frequency is directly measured by the IF counter and reflected in the TCXO frequency control.
This is to prevent the C side lock.

As described above, it is possible to provide a circuit for preventing the side lock during the AFC control even when the accuracy of the TCXO is deteriorated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), and a signal received from an antenna as an IF. And a voltage controlled oscillator (V) that generates an IF × N clock.
CO), a frequency error detection unit for detecting a frequency error from the IF signal, a frequency correction unit for performing frequency correction from the frequency correction pulse and outputting a corrected IF signal (AFCIF), and an AFCI for counting the AFCIF signal for a certain period of time.
The TCXO includes an F counter, an IF counter for counting an IF signal for a predetermined period, and a CPU for controlling a D / A converter for varying a voltage to the TCXO from the measurement result of the AFCIF counter and the IF counter. There is an effect that side lock during AFC control can be prevented even when accuracy deteriorates.

According to a second aspect of the present invention, there is provided a method for detecting and accumulating a frequency advance / delay from an IF signal output from an RF unit and outputting a frequency correction pulse; A by dividing by 1 and dividing by N + 1
Generating the FCIF signal, counting the generated AFCIF signal for a certain period of time for frequency measurement, calculating a correction value from the count value, and providing the D / A converter with the frequency of the temperature compensated crystal oscillator (TCXO). Controlling the frequency of the temperature compensated crystal oscillator (TCXO) and directly measuring the frequency of the IF signal for a certain period,
Detecting whether the temperature-compensated crystal oscillator (TCXO) is not side-locked, and adjusting the D / A converter controlling the temperature-compensated crystal oscillator (TCXO) when side-lock is detected AFC side lock prevention method comprising a step of preventing AFC side lock by writing the center value of AFC and returning to normal AFC control. Even if TCXO is deteriorated in accuracy, the AFC side lock is prevented. It has the effect that side lock can be prevented.

According to a third aspect of the present invention, there is provided a digital portable telephone device comprising the AFC side lock prevention circuit according to the first aspect, wherein the TCXO is degraded in accuracy. However, it has the effect that side lock during AFC control can be prevented.

An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a configuration of an AFC side lock prevention circuit according to an embodiment of the present invention. In FIG. 1, the AFC side lock prevention circuit is RF
And a temperature-compensated crystal oscillator (TCXO) 10 as a source oscillation of a voltage controlled oscillator (VCO), an RF unit 11 for down-converting a signal received from an antenna to an IF band,
Voltage controlled oscillator (VCO) for generating F × N clock
12, a frequency error detector 13 for detecting a frequency error from the IF signal, and a frequency corrector for correcting the frequency from the frequency correction pulse and outputting a corrected IF signal (AFCIF)
14 and AFCI to count AFCIF signal for a certain period
F counter 15 and IF for counting IF signal for a certain period
Counter 18, AFC IF counter 15, IF counter 18
And a CPU 16 for controlling a D / A converter 17 for varying the voltage to the TCXO 10 based on the measurement result.

The operation of the AFC side lock prevention circuit configured as described above will be described with reference to FIGS.

In FIG. 1, the IF output from the RF unit 11
The frequency error detection unit 13 detects and accumulates the leading and lagging of the frequency from the signal, and outputs a frequency correction pulse.

FIG. 2 shows the frequency advance / delay.
As shown in the figure, since the π / 4 shift QPSK modulation signal is demodulated, if the reception sensitivity is good, IF at the center of each quadrant
A signal is detected, but if the reception sensitivity is degraded and the frequency is shifted, the frequency is advanced, and the IF signal is detected at one of the two positions where the frequency is delayed.

The frequency corrector 14 normally divides the frequency of the IF × N clock generated by the voltage controlled oscillator (VCO) 12 by N. However, the frequency correction pulse from the frequency error detector 13 divides the frequency by N-1. Perform N + 1 frequency division to generate an AFCIF signal.

In normal AFC control, the AFCIF counter 15 measures the frequency of the AFCIF signal for a certain period,
PU 16 reads the value of AFCIF counter 15. CPU
16 is a D / A converter that calculates a correction value from the read value.
A value for controlling the frequency of the temperature-compensated crystal oscillator (TCXO) 10 is written in 17 to perform AFC control.

If the accuracy of the TCXO 10 is deteriorated, the frequency may be shifted to a position that greatly exceeds the quadrant that should originally exist in FIG. 2. AFC side lock occurs. The IF counter 18 directly measures the frequency of the IF signal for a certain period, and determines whether the temperature compensated crystal oscillator (TCXO) 10 is locked or not.
Can be detected.

When the AFC side lock is detected, C
The PU 16 prevents the side lock of the AFC by writing the adjusted center value to the D / A converter 17 which controls the temperature-compensated crystal oscillator (TCXO) 10, and the normal AFC
Control can be returned.

As described above, according to the embodiment of the present invention, a temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), and a signal received from an antenna are converted to an IF band. An RF unit that downconverts the signal to a voltage-controlled oscillator (V
CO), a frequency error detection unit for detecting a frequency error from the IF signal, a frequency correction unit for performing frequency correction from the frequency correction pulse and outputting a corrected IF signal (AFCIF), and an AFCI for counting the AFCIF signal for a certain period of time.
By providing an F counter, an IF counter that counts IF signals for a fixed period, and a CPU that controls a D / A converter that varies the voltage to TCXO based on the measurement result of each counter, AFC is performed even if the TCXO deteriorates in accuracy. Side lock can be prevented.

[0022]

As described above, according to the present invention, a temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO) and a signal received from an antenna are down-converted to an IF band. An RF unit, a voltage controlled oscillator (VCO) for generating an IF × N clock, a frequency error detection unit for detecting a frequency error from the IF signal, and a corrected IF signal (A
FCIF), an AFCIF counter that counts AFCIF signals for a certain period, an IF counter that counts IF signals for a certain period,
TCXO from IF counter and measurement result of IF counter
By providing a CPU that controls a D / A converter that varies the voltage to the
A circuit for preventing side lock during C control can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an AFC side lock prevention circuit according to an embodiment of the present invention;

FIG. 2 is a diagram for explaining AFC error correction;

FIG. 3 is a block diagram illustrating a configuration of a conventional AFC control circuit.

[Explanation of symbols]

 10, 30 Temperature Compensated Crystal Oscillator (TCXO) 11, 31 RF Unit 12, 32 Voltage Controlled Oscillator (VCO) 13, 33 Frequency Error Detector 14, 34 Frequency Corrector 15, 35 AFCIF Counter 16, 36 CPU 17, 37 D / A converter 18 IF counter

Claims (3)

[Claims] A temperature-compensated crystal oscillator (TCXO) serving as a source oscillation of an RF unit and a voltage controlled oscillator (VCO), an RF unit for down-converting a signal received from an antenna to an IF band, and an IF × N A voltage controlled oscillator (VCO) for generating a clock, a frequency error detection unit for detecting a frequency error from the IF signal, a frequency correction unit for correcting the frequency from the frequency correction pulse and outputting a corrected IF signal (AFCIF), An AFCIF counter for counting the AFCIF signal for a certain period of time; an IF counter for counting the IF signal for a certain period of time;
A comprising a CPU for controlling the A converter.
FC side lock prevention circuit. 2. A step of detecting and accumulating a lead / lag of a frequency from an IF signal output from an RF unit and outputting a frequency correction pulse;
Performing N + 1 frequency division to generate an AFCIF signal;
The generated AFCIF signal is counted for a certain period for frequency measurement, a correction value is calculated from the count value, and D
A value for controlling the frequency of the temperature-compensated crystal oscillator (TCXO) is written into the / A converter and the temperature-compensated crystal oscillator (TC
XO) frequency, and the frequency of the IF signal is directly measured for a certain period of time to obtain a temperature-compensated crystal oscillator (TCX).
O) detecting whether side lock has occurred, and, if side lock is detected, writing an adjusted center value to a D / A converter controlling a temperature compensated crystal oscillator (TCXO). A step of preventing AFC side lock and returning to normal AFC control. 3. A digital portable telephone device comprising the AFC side lock prevention circuit according to claim 1.