JP4199899B2 - Tuning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for correcting a tuning error of a tuning circuit in an RF front end circuit.
[0002]
[Prior art]
FIG. 4 is a block diagram showing an example of a conventional tuning method.
In the RF front end circuit 100 ′, the RF signal (radio signal) input from the input terminal is amplified by the AGC amplifier (AGCAMP) 1 and enters the tuning circuit 2. The tuning circuit 2 is composed of a PLL circuit A in the subsequent stage (a local oscillation circuit 5, a 1 / n frequency divider 6, a phase comparator 8, a 1 / N frequency divider 9, a reference oscillator 10 and an LPF 11 in a broken line frame in FIG. ) Resonates at the center frequency of the input signal.
[0003]
The signal passing through the tuning circuit 2 is mixed with a local signal (local signal) oscillated from a local oscillator 5 by a mixer (MIX) circuit 3 and taken out as an IF signal (intermediate signal) through a BPF 4.
[0004]
On the other hand, the control signal corresponding to the preset frequency of the receiver is output from the microcomputer (microcomputer) 7 as the local oscillation signal, and the frequency division ratio of the frequency divider 6 is made variable and divided by n. A voltage (tuning voltage) obtained by performing phase comparison between the n-divided signal and the frequency obtained by dividing the signal of the reference oscillator 10 by N with the frequency divider 9 with the phase comparator 8 and smoothing the difference with the LPF 11. ) Is fed back to the local oscillation circuit 5 and the tuning circuit 2 to be tuned to the input signal frequency.
[0005]
[Problems to be solved by the invention]
The oscillation frequency of the resonant local oscillation circuit of the tuning circuit 2 is normally changed by configuring the LC circuit 50 as shown in FIG. 5 and controlling the capacitance of the variable capacitance diode 51 with the tuning voltage. However, there is a problem that the tuning frequency of the tuning circuit 2 may be shifted due to variations in the non-linear region of the variable capacitance diode 51 (see FIG. 3) and variable capacitance diodes (variable capacitance elements), and accurate tuning may not be performed. It was.
[0006]
The present invention has been made in order to solve the problems in the conventional tuning circuit described above, and obtains a stable tuning characteristic within the reception band by correcting the tuning deviation caused by the non-linearity of the element and variations in characteristics. The purpose is to provide a tuning method.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a tuning device according to a first aspect of the present invention is a tuning means for controlling a tuning frequency based on a tuning signal, a tuning frequency from the tuning means and a tuning signal are inputted, and a deviation in tuning deviation of the tuning means is detected. A correction voltage generating means for detecting a voltage corresponding to a minute and generating a correction voltage; and a correction means for correcting the tuning signal based on the correction voltage generated by the correction voltage generating means, The means includes a frequency oscillator that outputs a frequency signal in a frequency range before and after the tuning frequency corresponding to the tuning signal, a tuning signal from the tuning means, and a frequency signal from the frequency oscillator as inputs, and an input signal as and synthesizing for synthesizing means, means for generating a correction voltage based on the output signal from the combining means, further comprising a, wherein.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the RF front end circuit of the present invention, the correction voltage obtained by the correction voltage generation circuit C of the present invention is added to the tuning voltage generated by the conventional method (PLL circuit B in FIG. 1) during the tuning process of the received radio frequency signal. Then, by controlling the tuning circuit, the tuning deviation caused by the variation of the elements such as the variable capacitance diode described above is corrected, and a stable tuning characteristic is obtained within the reception band.
[0011]
FIG. 1 is a block diagram showing an embodiment of a front end circuit to which the tuning system of the present invention is applied.
The RF front end circuit 100 includes an intermediate frequency signal system A including an AGC amplifier 21, a tuning circuit 22, a mixer (MIX1) circuit 23, and a BPF 24, a local oscillation circuit 25, a 1 / n frequency divider 26, a phase comparator 28, PLL circuit B (same configuration as PLL circuit A in FIG. 4) comprising 1 / N frequency divider 29, reference oscillator 30 and LPF 31, voltage controlled oscillation circuit (VCO circuit) 32, mixer (MIX2) circuit 33, LPF 34, A correction voltage generation circuit C comprising an A / D converter 35, a memory 36 and a level comparator 37, a microcomputer 27 for giving a control signal corresponding to the preset frequency of the receiver to the PLL circuit B, and a PLL circuit B An adder that adds the output (tuning voltage) and the output (correction voltage) of the correction voltage generation circuit C to the tuning circuit 22 38.
[0012]
Hereinafter, the operation of the RF front end circuit 100 will be described.
An RF signal (wireless signal) input from the input terminal is amplified by an AGC amplifier (AGCAMP) 21 and enters a tuning circuit 22. The tuning circuit 22 resonates at the center frequency of the input signal by the output voltage from the adder 38 in the subsequent stage (the addition result of the tuning voltage generated by the PLL circuit B and the correction voltage generated by the correction voltage generation circuit C). The tuning voltage generated by the PLL circuit B is given to the correction voltage generation circuit C.
Further, the signal passing through the tuning circuit 22 is mixed with a local oscillation signal oscillated from a local oscillator 25 by a mixer (MIX) circuit 23 and taken out as an IF signal (intermediate signal) through a BPF 42.
[0013]
On the other hand, as the local signal, a control signal corresponding to the preset frequency of the receiver is outputted from the microcomputer 27 and given to the PLL circuit B. In the PLL circuit B, the control signal output from the microcomputer 27 divides the frequency by n while changing the frequency dividing ratio of the frequency divider 26. This n-divided signal is a voltage (tuning voltage) obtained by comparing the phase of the signal of the reference oscillator 30 by N with the frequency divider 29 and the phase comparator 28 and smoothing the difference with the LPF 31. Is fed back to the local oscillation circuit 25 and the adder 38.
[0014]
Further, the output signal of the tuning circuit 22 is taken out at point a and applied to the correction voltage generation circuit C. As will be described later, the correction voltage generation circuit C detects the voltage deviation ΔV based on the tuning voltage generated by the PLL circuit B and the output from the tuning circuit 22 and outputs a correction voltage based on this voltage difference ΔV. 38.
[0015]
(Operation of the correction voltage generation circuit C)
The output signal of the tuning circuit 22 taken out at the point a is input to the mixer circuit 33 by the correction voltage generation circuit C. Further, the output signal of the voltage controlled oscillation circuit 32 with a sweep function (the voltage controlled oscillation circuit 32 inputs the tuning voltage output from the PLL circuit B) is input to the other input terminal of the mixer circuit 33.
[0016]
The voltage controlled oscillation circuit 32 changes the oscillation frequency by changing the tuning voltage, as with the local oscillation circuit 25, but the local oscillation circuit 25 vibrates at the frequency of the sum (or difference) of the RF signal frequency and the IF signal frequency. On the other hand, this circuit is set to oscillate at the same frequency as the RF signal frequency. Further, as shown in FIG. 3, the frequency is swept in steps within a range of ± f around the center frequency fc of the RF signal. Let
[0017]
The mixer circuit 33 mixes the output signal of the tuning circuit 22 described above with the output of the voltage controlled oscillation circuit 32 and the mixer circuit 33, and inputs the output to the LPF 34.
The LPF 34 extracts the level (voltage value) for each frequency at each step with the center frequency fc of the RF signal as shown in FIG.
The output of the LPF 34 is A / D converted by the A / D converter 35 and taken into the memory 36. The level comparator 37 shifts the level (voltage value) of the center frequency fc within a range of ± f with respect to the center frequency fc. Compare the level (voltage value). In this case, as shown in FIG. 2, if the signal is accurately tuned, the signal level peaks at fc and the correction voltage becomes 0 (zero). However, if the signal is not tuned and there is a peak at fc + f1, Since this deviation ΔV is detected, this is used as a correction voltage. The output (correction voltage) of the level comparator 37 is input to the adder 38, and is added to the tuning voltage from the PLL circuit B by the adder 38, and the variable capacitance diode 51 of the resonance local oscillation circuit of the tuning circuit 22 (FIG. 5). To be applied. Thereby, the variable diode 51 is controlled by the output voltage of the adder circuit, and the tuning deviation is corrected.
[0018]
Note that the sweep frequency range of the voltage-controlled oscillation circuit 32 and the step of the frequency to be changed take into consideration the characteristics of the element (variable capacitance diode) used in the resonance local oscillation circuit of the tuning circuit, the actual bandwidth, and the tuning circuit. Set. Further, once the receiver tuning is set, it does not change frequently, and no special high-speed processing is required. As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, It cannot be overemphasized that various deformation | transformation implementation is possible.
[0019]
【The invention's effect】
As explained above, according to this onset bright, in the tuning device (RF front-end circuit), since by detecting the shift amount of the tuning of the tuning means it is provided a correction voltage generating means for generating a correction voltage, the conventional A tuning shift that cannot be processed by tuning only the tuning voltage generated by the PLL circuit of the type can be detected and corrected. Thereby, a stable tuning characteristic can be obtained over the entire reception band to be used.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an RF front-end circuit to which a tuning method of the present invention is applied.
FIG. 2 is an explanatory diagram of a shift in tuning characteristics.
FIG. 3 is an explanatory diagram of a sweep characteristic of a VCO circuit (voltage controlled oscillation circuit) used in the present invention.
FIG. 4 is a block diagram showing a configuration example of an RF front end circuit to which a conventional tuning method is applied.
FIG. 5 is a diagram illustrating a configuration example of a resonance local oscillation circuit of a tuning circuit.
6 is an explanatory diagram of a change in capacitance of a variable capacitance diode used in the resonant local oscillation circuit of FIG. 5;
[Explanation of symbols]
22 Tuning circuit 32 VCO circuit (voltage controlled oscillation circuit)
33 Mixer circuit (variable capacitance element)
38 Adder (correction means)
100 RF front-end circuit (tuning device)
C correction voltage generation circuit

Claims (1)

Tuning means for controlling the tuning frequency based on the tuning signal;
A correction voltage generating means for inputting a tuning frequency from the tuning means and the tuning signal, detecting a voltage corresponding to a deviation of the tuning deviation of the tuning means, and generating a correction voltage;
Correction means for correcting the tuning signal based on the correction voltage generated by the correction voltage generation means,
The correction voltage generating means includes
A frequency oscillator that outputs a frequency signal in a frequency range before and after the tuning frequency corresponding to the tuning signal, and
A synthesizing unit that inputs a tuning signal from the tuning unit and a frequency signal from the frequency oscillator, and synthesizes an input signal;
Means for generating a correction voltage based on an output signal from the synthesizing means,
A tuning device characterized by.

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