JP2006229427A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that receiving sensitivity is deteriorated due to shift of a resonant frequency generated due to a stray capacity when a discriminator is connected to a detection IC in configuring an FM/FSK receiver of a weak radio or small power facility using the detection IC. <P>SOLUTION: A discriminator circuit 6b consists of a piezoelectric resonator X1, a resistor R1, a capacitance C1, a varactor diode VC and a capacitance C2. A level detecting circuit 8 for monitoring detection output is connected to an AF-OUT terminal of a detection Ic7. A control voltage to be applied to the varactor diode VC is changed while the level detecting circuit 8 is monitoring the detection output of the AF-OUT terminal in a state where a high-frequency signal of a constant level is input from an RF input terminal, and the control voltage at which the detection level is the maximum is stored in a memory 9. The control voltage stored in the memory 9 is applied to the varactor diode VC1 via the resistor R1 simultaneously with operation start of a receiver 110. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an FM / FSK receiver for weak wireless or low power equipment, and more particularly to an FM / FSK receiver improved in reception sensitivity by improving the characteristics of a discriminator circuit.

Conventionally, short-distance FM voice communication and FSK data communication using weak radio or low-power radio equipment do not require a license to use a frequency for operating a radio station, and can configure a communication system at low cost. Because of its advantages, it is used in a wide range of fields such as keyless entry, wireless speakers, and game machines.

FIG. 4 is a diagram showing an example of a receiving apparatus compatible with conventional FM / FSK, and FIG. 4A is a schematic configuration diagram. As shown in the figure, the receiving apparatus 10 includes an antenna 1, an RF input circuit 2 including an RF bandpass filter 2a, an RF amplifier 3, a mixer 4a, a frequency multiplication unit 4b, and a local oscillation circuit 4c. A detection unit comprising a frequency conversion unit 4, an IF amplification unit 5 comprising an IF bandpass filter 5a and an IF limiter amplifier 5b, a detection unit 6a, a discriminator circuit 6e, a detection low-pass filter (active filter) 6c, and a comparator 6d. And an output unit 6.

In the figure, the FM / FSK received radio wave received by the antenna 1 is selected in a predetermined frequency band by the RF band pass filter 2a of the RF input circuit 2, and is level-amplified by the RF amplifier 3, and the mixer of the frequency converting unit 4 It is output to one input terminal of 4a.
The oscillation output of the local oscillation circuit 4c multiplied to a predetermined frequency by the frequency multiplication unit 4b is input to the other input terminal of the mixer 4a.
A received wave (hereinafter referred to as an IF received wave) frequency-mixed with the frequency multiplier 4b output signal in the mixer 4a and converted to a predetermined intermediate frequency is output to the IF bandpass filter 5a of the IF amplifier 5.

The IF reception wave from which the unnecessary wave is removed by the band pass filter 5a is amplified to a predetermined level by the IF limiter amplifier 5b and output to the detection output unit 6.
The IF reception wave input to the detection output unit 6 is subjected to FM detection in the detection unit 6a using the discriminator circuit 6e as a phase shift circuit.
From the detection output of the detection unit 6a, a high-frequency component is removed by a low-pass filter (active filter) 6c for detection and output to the comparator 6d. The waveform is shaped by the comparator 6d and a demodulated signal is taken out from the DATA-OUT terminal in the figure. . The detection output signal can be directly taken out from the AF-OUT end of the figure connected to the output circuit of the detection unit 6a.

In order to reduce the size, the receiving apparatus 10 having the above-described configuration includes, for example, the RF amplifier 3, the mixer 4a, the frequency multiplication unit 4b, the IF limiter amplifier 5b, the detection unit 6a, the detection low-pass filter (active filter) in FIG. ) A small-sized general-purpose FM / FSK-compatible detection IC (hereinafter simply referred to as a detection IC) including a filter amplifier (not shown) 6c and a comparator 6d is provided on the market.

FIG. 4B is a schematic configuration diagram of an FM / FSK-compatible receiving device in which the receiving device 10 is configured using the detection IC.
As shown in the figure, the FM / FSK receiver 10a includes an antenna 1, an RF input circuit 2 including an RF bandpass filter 2a, a local oscillator 4c, an IF bandpass filter 5a, and a discriminator circuit. 6e, a CR constant circuit 6c1 of a detection low-pass filter (active filter) 6c, and a detection IC 7.
The other components other than the detection IC 7 are connected to predetermined connection terminals of the detection IC 7 to constitute the receiving device 10a. It should be noted that the respective components included in the detection IC 7 are omitted for simplicity.
The receiving apparatus 10a having the above configuration is a receiving apparatus having the same functional operation as the receiving apparatus 10 in FIG.
Toshiba Bipolar Linear Integrated Circuit Silicon Monolithic TA31275FN, TA31275FNG Data Sheet

Weak radio or low-power radio stations do not require a license to use the frequency and can easily configure the system. On the other hand, since the transmission output is regulated low by the Radio Law, users can extend the communication distance. In order to improve the convenience of the receiver, it is strongly desired to improve the reception sensitivity characteristic.
However, an external component constituted by a resonance circuit or the like externally attached to the detection IC, for example, the discriminator circuit 6e as a phase shift circuit has a resonance frequency due to a stray capacitance or the like when connected to the detection IC. There is a case in which the value deviates from a predetermined value, which causes a problem that the receiving sensitivity of the receiving apparatus is lowered.
In addition, there is a problem in that reception sensitivity is deteriorated due to interference by transmission radio waves of other radio stations in the nearby frequency.
The present invention has been made to solve the above-described problem, and an object thereof is to provide an FM / FSK-compatible receiving device having excellent reception sensitivity characteristics.

In order to solve the above problems, in claim 1, an antenna, a high frequency amplifier circuit, a frequency converter, an intermediate frequency amplifier circuit, a detection circuit including a discriminator circuit, a detection low pass filter, a comparator, , An FM / FSK compatible receiving device,
The discriminator circuit is composed of a parallel circuit of a piezoelectric resonator forming a series resonance circuit, a resistor, and a variable capacitance element, and the frequency-amplitude characteristic of the discriminator circuit varies depending on the values of the resistance and the variable capacitance element. To do,
A control applied to the variable capacitance element when the output level of the detection circuit is maximized by applying a high-frequency input signal of a certain level to the FM / FSK compatible receiving device and applying a control voltage to the variable capacitance element. A memory is provided that stores a voltage.

Further, in claim 2, the FM / FSK-compatible receiving device according to claim 1,
The control voltage stored in the memory is applied to the variable capacitance element at the start of the operation of the FM / FSK compatible receiver.

According to a third aspect of the present invention, in the FM / FSK-compatible receiving device according to the second aspect, when the output level of the detection circuit at the time of reception reaches a saturation level, a control voltage is applied to the variable capacitance element. Thus, the detection circuit output level is configured to be a preset level.

In claim 4, an antenna, a high frequency amplifier circuit, a frequency converter, an intermediate frequency amplifier circuit including an intermediate frequency bandpass filter, a detector circuit including a discriminator circuit, a low pass filter for detection, a comparator, And an FM / FSK-compatible receiving device,
The discriminator circuit is composed of a parallel circuit of a piezoelectric resonator forming a series resonant circuit, a resistor, and a variable capacitance element, and adjusting the value of the resistor connected in parallel to the piezoelectric resonator of the discriminator circuit. The linear region of the frequency vs. amplitude characteristic of the discriminator circuit has the same width as the 3 dB passband width of the intermediate frequency bandpass filter.

According to the first and second aspects of the present invention, in the FM / FSK-compatible receiving device, a control voltage is applied to the variable capacitance element of the discriminator circuit by applying a high-frequency input signal at a constant level, and the output level of the detection circuit is maximized The control voltage applied to the variable capacitor at the time is stored in the memory, and the control voltage stored in the memory is applied to the variable capacitor when the operation of the receiving apparatus is started.
As a result, the resonance frequency shift of the discriminator circuit due to stray capacitance or the like when the discriminator circuit is connected to the detection unit of the detection IC is corrected, and as a result, the reception sensitivity of the receiving device is improved.

According to a third aspect of the present invention, in the receiving device according to the first and second aspects, when the output level of the detection circuit reaches a saturation level due to a strong electric field interference wave, the variable capacitance element of the discriminator circuit is used. By applying the control voltage to shift the center frequency of the discriminator circuit, the reception sensitivity of the interference wave is lowered, and the sensitivity suppression from the interference wave of the desired reception wave is reduced, thereby substantially reducing the reception device. The reception sensitivity of the desired wave can be improved.
Furthermore, in the invention of claim 4, the value of the damper resistor connected in parallel to the piezoelectric resonator of the discriminator circuit is adjusted, and the linear region of the frequency versus amplitude characteristic of the discriminator circuit is It was confirmed that the S / N of the discriminator circuit was improved and the reception sensitivity of the receiving apparatus was improved by about 1 dB by setting the same width as the 3 dB pass bandwidth of the bandpass filter.
Therefore, according to the present invention, the FM / FSK compatible receiving apparatus having excellent receiving sensitivity characteristics is remarkably effective.

The present invention will be described based on the embodiments shown in the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an FM / FSK-compatible receiving apparatus using a weak radio or low power radio facility according to the present invention.
As shown in the figure, the receiving apparatus 100 includes an antenna 1, a high-frequency input circuit 2 including an RF bandpass filter 2a, a local oscillator 4c, an IF bandpass filter 5a, and a discriminator circuit 6b. A detection low-pass filter (active filter) CR constant circuit 6c1, an FM / FSK compatible detection IC (hereinafter simply referred to as a detection IC) 7, a level detection circuit 8, and a memory 9.
The detection IC 7 is the same detection IC as the detection IC 7 of the receiving device 10a in FIG.

The receiving apparatus 100 employs the discriminator circuit 6b shown in FIG. 1 in place of the discriminator circuit 6e in the conventional receiving apparatus 10a shown in FIG. 4B, and further includes an AF-OUT terminal of the detection IC 7 and The level detection circuit 8 and the memory 9 are connected between the discriminator circuit 6b.
The demodulation operation of the receiving apparatus 100 is the same as the receiving operation of the receiving apparatus 10a of FIG. 4B except for the operations of the discriminator circuit 6b, the level detection circuit 8, and the memory. Description of is omitted.

As shown in FIG. 1, the discriminator circuit 6b of the receiving apparatus 100 includes a piezoelectric resonator X1, a damper resistor R1, a capacitor C1, a varactor diode (variable capacitor) VC, and a series circuit of a capacitor C2. Have a circuit configuration connected in parallel. The capacitor C3 is a capacitor for removing high frequency components of the power supply (Vcc) circuit.
The varactor diode VC is supplied with a control voltage from the memory 9 via a resistor R2 connected to a connection midpoint between the capacitor C1 and the varactor diode VC. The resistor R3 is a return circuit resistor for the control voltage.
The level detection circuit 8 is connected to the AF-OUT terminal of the detection IC 7 and detects the detection output level of the receiving apparatus 100.

Prior to use of the receiving apparatus 100 having the above configuration, the detection output level of the detection unit 6a is detected by the level detection circuit 8 connected to the AF-OUT terminal in a state where a high-frequency signal of a constant level is input from the antenna input terminal in the figure. The control voltage is applied to the varactor diode VC while monitoring the control voltage, and the control voltage that maximizes the detection output level is stored in the memory 9.
Simultaneously with the start of the operation of the receiving apparatus 100, the control voltage stored in the memory 9 is applied to the varactor diode VC via the resistor R2.
With this configuration, it is possible to correct a deviation from the best sensitivity point of the resonance frequency of the piezoelectric resonator X1 caused by stray capacitance or the like when the discriminator circuit 6b is connected to the detection IC 7. The receiving sensitivity of 100 can be improved.

FIG. 2 is a schematic configuration diagram of an FM / FSK-compatible receiving apparatus using a weak radio or a low-power radio station that prevents a decrease in reception sensitivity of a desired RF received wave due to a nearby interference wave.
As shown in the figure, the receiving apparatus 100a includes an antenna 1, a high-frequency input circuit 2 including an RF bandpass filter 2a, a local oscillator 4c, an IF bandpass filter 5a, a discriminator circuit 6b, A detection low-pass filter (active filter) CR constant circuit 6c1, an FM / FSK compatible detection IC (hereinafter simply referred to as a detection IC) 7, a level detection circuit 8a, and a memory 9a are included.
The receiving apparatus 100a has a circuit configuration in which the level detecting circuit 8 and the memory 9 in the receiving apparatus 100 shown in FIG. 1 are replaced with the level detecting circuit 8a and the memory 9a, respectively. Since the receiving operation is the same as the receiving operation of the receiving apparatus 100 of FIG. 1 except for the operations of the discriminator circuit 6b, the level detection circuit 8a, and the memory 9a, the description of the operation of the common part is omitted.

Here, the level detection circuit 8a and the memory 9a of the receiving device 100a, when starting the operation, store the control voltage that optimizes the receiving sensitivity of the receiving device 100a stored in the same procedure as that of the receiving device 100 of FIG. The voltage is applied to the varactor diode VC of the discriminator circuit 6b and operates as follows.
During the operation of the receiving apparatus 100a, for the desired received wave received at the normal level, the output level of the detector 6a at the AF-OUT end monitored by the level detection circuit 8a is in the linear region of the received input versus detected output characteristics. However, when a disturbing wave having a strong electric field is received, the output level of the detection unit 6a monitored by the level detection circuit 8a becomes saturated.

The control voltage from the memory 9a by the control from the level detection circuit 8a that has detected this saturation state causes the detection level of the output of the detection unit 6a in the level detection circuit 8a to be a predetermined level in the linear region via the resistor R2. And applied to the varactor diode VC of the discriminator circuit 6b.
The applied control voltage changes the capacitance value of the varactor diode VC connected in parallel to the piezoelectric resonator X1, shifts the resonance point of the discriminator circuit 6b from the sensitivity best point, and reduces the sensitivity suppression effect due to the interference wave. Let
By configuring as described above, it is possible to substantially improve the reception sensitivity of the desired wave of the reception device 100a.

Other means for improving reception sensitivity in the FM / FSK-compatible receiving apparatus having the configuration shown in FIG. 1 are as follows.
In the FM / FSK receiver of FIG. 1, the local oscillator 4c is set to have a predetermined frequency accurately, and the center frequency of the discriminator circuit 6b is set to be the best sensitivity of the receiver. Thereafter, the resistor connected in parallel to the piezoelectric resonator X1 of the discriminator circuit 6b so that the linear region of the frequency vs. amplitude characteristic of the discriminator circuit 6b matches the 3 dB pass bandwidth of the IF bandpass filter 5a (not shown). Adjust R1.
FIG. 3 is a characteristic diagram showing an example of the frequency-amplitude characteristic of the discriminator circuit 6b. FIG. 3A shows the characteristic when the resistance R1 = 47 kΩ after the above adjustment, and FIG. 3B shows the adjustment. The characteristic when the previous R1 = 3.9 kΩ is shown. As shown in the figure, the adjustment reduces the characteristic bandwidth and increases the output signal level, thereby improving the S / N of the circuit and improving the sensitivity by 1.1 dB. confirmed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing an embodiment of an FM / FSK-compatible receiving device using a weak radio or low power radio station according to the present invention. 1 is a schematic configuration diagram of an FM / FSK-compatible receiving device using a weak radio or a low-power radio station that prevents a decrease in reception sensitivity of a desired RF received wave due to a nearby interference wave according to the present invention. FIG. 4 is a characteristic diagram illustrating an example of frequency versus amplitude characteristics of a discriminator circuit, where (a) is a characteristic diagram after adjustment of the parallel resistance value of the discriminator circuit, and (b) is a characteristic diagram before adjustment. It is a figure which shows an example of the conventional FM / FSK corresponding | compatible receiving apparatus by a weak radio | wireless or a low electric power radio station, (a) is a structure schematic diagram, (b) is a general purpose FM / FSK with the circuit structure of (a). The structure schematic diagram comprised using corresponding detection IC.

Explanation of symbols

1 .. Antenna 2. RF input circuit 2a RF band pass filter 3. RF amplifier 3
4. Frequency converter 4a Mixer 4b Frequency multiplier 4c Local oscillator
5. IF amplifier, 5a IF band-pass filter, 5b IF limiter amplifier,
6 .... detection output unit, 6a ... detection unit, 6b ... discriminator circuit,
6c ・ ・ Low-pass filter for detection (active filter),
6c1 .. CR constant circuit of low-pass filter for detection, 6d .. Comparator,
6e · Discriminator circuit, 7 · · FM / FSK compatible detection IC,
8, 8a ··· level detection circuit, 9, 9a · · memory, 10 · · FM / FSK receiver,
10a ··· FM / FSK receiver configured using a detection IC, 100 · · FM / FSK receiver,
C1, C2, C3 .. capacity, R1, R2, R3 .. resistance,
VC ·· Varactor diode (variable capacitance element), X1 · · Piezoelectric resonator

Claims (4)

An FM / FSK compatible receiver comprising an antenna, a high-frequency amplifier circuit, a frequency converter, an intermediate frequency amplifier circuit, a detector circuit including a discriminator circuit, a low-pass filter for detection, and a comparator. There,
The discriminator circuit is composed of a parallel circuit of a piezoelectric resonator forming a series resonance circuit, a resistor, and a variable capacitance element, and the frequency-amplitude characteristic of the discriminator circuit varies depending on the values of the resistance and the variable capacitance element. To do,
A control applied to the variable capacitance element when the output level of the detection circuit is maximized by applying a high-frequency input signal at a certain level to the FM / FSK compatible receiver and applying a control voltage to the variable capacitance element. An FM / FSK-compatible receiving device comprising a memory storing a voltage. 2. The FM / FSK-compatible receiving device according to claim 1, wherein the control voltage stored in the memory is applied to the variable capacitance element at the start of operation of the FM / FSK-compatible receiving device. 3. . When the output level of the detection circuit at the time of reception reaches a saturation level, a control voltage is applied to the variable capacitance element so that the detection circuit output level becomes a preset level. The FM / FSK-compatible receiving device according to claim 2. FM comprising an antenna, a high frequency amplifier circuit, a frequency converter, an intermediate frequency amplifier circuit including an intermediate frequency bandpass filter, a detector circuit including a discriminator circuit, a low pass filter for detection, and a comparator / FSK compatible receiving device,
The discriminator circuit is composed of a parallel circuit of a piezoelectric resonator forming a series resonant circuit, a resistor, and a variable capacitance element, and adjusting the value of the resistor connected in parallel to the piezoelectric resonator of the discriminator circuit. The linear region of the frequency vs. amplitude characteristic of the discriminator circuit has the same width as the 3 dB passband width of the intermediate frequency bandpass filter. FM / FSK compatible receiver.

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