JP2600451Y2 - Receive signal mixing circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception signal mixing circuit, and more particularly, to a reception signal mixing circuit in a transmission / reception system for a wireless communication device, in particular, a cordless telephone device.

[0002]

2. Description of the Related Art A reception signal mixing circuit (hereinafter, referred to as a mixer circuit) of a reception block in a conventional transmission / reception system for a cordless telephone has a configuration shown in FIG. That is, FIG. 2 is a block diagram of a transmission / reception system for a cordless telephone device, where A is a transmission block, B is a reception block,
C is a transmission or reception channel switching block. The transmission block A includes an audio amplification circuit A1 for amplifying the audio input input from the audio input terminal Tin, and a compression circuit for compressing the change range of the amplitude of the audio signal to increase the degree of modulation and improve the S / N ratio. A2, an intermediate circuit A3 including a confidential circuit, a limiter for waveform shaping, a low-pass filter for removing harmonics, and a displacement adjusting circuit for adjusting the displacement width of the signal, and a carrier of a predetermined channel (in this case, fc = 3
A modulation circuit A4 that modulates the input signal (80 MHz) with an input signal, and a final-stage amplifier A5 are sequentially connected in series. And f
The signal using c as the carrier is supplied to the antenna X via the branching circuit 1. As described above, the audio input input from the terminal Tin by each circuit is placed on the carrier fc of a predetermined channel and transmitted via the antenna X.

[0003] Next, the receiving block B passes through the demultiplexing circuit 1 to divide the signal supplied from the antenna X into a required frequency band (fa = 254 MHz in this case).
(A frequency band centered at the center) is input. The reception block B mixes the first local frequency fb supplied from the first local oscillation circuit 4 via the buffer amplifier 5 with the RF (radio frequency) amplifier circuit 2, the RF bandpass filter 3, and the reception signal fa. A first mixing circuit (mixer circuit) 6, an IF (intermediate frequency) band-pass filter 7, an IF amplifier circuit 8, a second local oscillator circuit A second mixing circuit 10 that obtains a second intermediate frequency having a difference between both frequencies as a beat by mixing the second local frequency supplied from 9 and the first intermediate frequency, and an IF bandpass filter or an IF amplifier circuit. , A detection and demodulation circuit 12 for extracting a voice signal from the second intermediate frequency, a voice low-pass filter, a confidential speech circuit, a voice amplification circuit, and a signal whose amplitude is compressed during transmission. Circuit 1 consisting expansion circuit to return the waveform based on
3 and an output amplifier circuit 14 are sequentially connected. An audio signal is extracted from a carrier centered on fa received by the antenna X via these circuits. Note that t
1 is a signal receiving terminal, t2 and t3 are channel switching block connection terminals, t4 is a receiving block output terminal, t5 is a power supply terminal (Vcc), and t6 is a common terminal (GRD).

The mixer circuit 6 comprises an NPN transistor Q1, resistors R1 to R4, capacitors C1 to C3, and a tuning circuit LC. According to FIG. 2, in the mixer circuit 6, the base of the transistor Q1 is connected to the signal input terminal 61, and the collector thereof is connected to the power supply terminal t5 via the tuning circuit LC composed of a parallel circuit of the IF transformer L1 and the capacitor C1. Connected and the emitter is a resistor R
3 and a common terminal t6 via a parallel circuit of the capacitor C2.
It is connected to the. A resistor R1 is connected between the base and the collector of the transistor Q1, and a resistor R2 is connected between the base of the transistor Q1 and the common terminal 2. Further, a resistor R4 is connected between the collector of the transistor Q1 and the signal output terminal 62, and the signal output terminal 62
And a common terminal t6, a capacitor C3 is connected.

On the other hand, the IF band pass filter 7 takes in the signal output from the collector of the transistor Q1 to the filter CF1 via the resistor R4 and the signal output terminal 62,
Its output terminal is connected via a resistor 5 to an IF amplifier circuit 8 at the subsequent stage. The output side of the resistor R5 is connected to the common terminal 2 via the capacitor C4.

In such a mixer circuit 6 of FIG. 2,
In the state where the power supply voltage Vcc is applied between the power supply terminal t5 and the common terminal t6, when a high frequency signal (RF signal) in which two frequencies are overlapped and mixed is input to the signal input terminal 61, that is, the antenna X is When the reception signal fa sent via the first local oscillation circuit 4 and the first local frequency fb supplied via the first local oscillation circuit 4 are mixed and input, the transistor Q1 is turned on, and the tuning transformer, that is, the IF transformer L1 and the capacitor are turned on. Tuning is performed by a tuning circuit (parallel resonance circuit) composed of C1 to operate so as to obtain a first intermediate frequency IF (for example, 21.7 MHz) of a difference between the two frequencies fa and fb, and is sent to the next-stage filter CF1. The selectivity Q of the tuning circuit determines the quality of the characteristic. When the selectivity Q increases, only the signal component is amplified and the other components are attenuated. Therefore, it is usually necessary to design the Q value to be high. However, at this time, the tuning circuit LC has its selectivity Q
It is set so that impedance matching with the circuit including the F band pass filter 7 can be achieved. Filter CF1
Is a high-pass filter that passes a high frequency of 10.7 MHZ or more. The high-pass filter outputs the passed high-frequency signal to an amplifying transistor (not shown) of the IF amplifier circuit 8 in the next stage, and amplifies the signal. To be sent to the server.

[Problems to be solved by the invention]

However, such a circuit configuration of the conventional mixer circuit 6 has the following problems.
In the conventional example shown in FIG. 2, a tuning circuit LC including a tuning coil and a capacitor is used.
Is input, there is a disadvantage that mismatch of selectivity Q is likely to occur with a circuit in the subsequent stage, and a disadvantage that the circuit configuration becomes large and the cost is increased. Had become. It is an object of the present invention to eliminate the above-mentioned conventional problems, to obtain a stable selectivity Q even when a strong received signal fa is input, and to provide a mixer circuit having a simple circuit configuration and good impedance matching. Is to provide.

[0008]

In order to achieve the above object, the present invention provides a reception signal mixing circuit in a cordless telephone apparatus transmission / reception system, which includes a reception signal fa of a required frequency band inputted via an antenna and a local signal. A signal input terminal for mixing and superimposing and inputting two high-frequency signals having an oscillation frequency fb, an NPN transistor having a base connected to the signal input terminal, and a first transistor connected between a base and a collector of the NPN transistor A resistor and the NPN
A second resistor connected between a base of the transistor and a common terminal; an impedance matching resistor connected between a collector of the NPN transistor and a power supply terminal; and an insertion connection between a collector of the NPN transistor and a signal output terminal. And a first resistor connected between the emitter and the common terminal of the NPN transistor.
And a second resistor connected between the signal output terminal and the common terminal, and extracts a predetermined intermediate frequency by mixing the reception signal fa and the local oscillation frequency fb. It is characterized in that the signal is passed through the next-stage crystal filter via the signal output terminal and then transmitted to the subsequent detection circuit.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 1 shows a mixer circuit 6 showing an embodiment of the present invention.
1 is a block diagram of a transmission / reception system for a cordless telephone device including a circuit configuration diagram of A, where A is a transmission block, B is a reception block, and C is a transmission or reception channel switching block. 1, the same reference numerals as those in FIG. 2 denote the same items. C5 is a capacitor, and R0 and R6 are resistors.
The transmission block A includes an audio amplification circuit A1 for amplifying the audio input input from the audio input terminal Tin, and a compression circuit for compressing the change range of the amplitude of the audio signal to increase the degree of modulation and improve the S / N ratio. A2, and an intermediate circuit A3 including a confidential circuit, a limiter for waveform shaping, a low-pass filter for removing harmonics, and a displacement adjusting circuit for adjusting the displacement width of the signal.
And a carrier of a predetermined channel (fc = 380 in this case)
MHz) with an input signal, and a final-stage amplifier A5 are sequentially connected in series. Then, a signal using fc as a carrier wave is supplied to the antenna X via the branching circuit 1. Thus, the terminal T
The voice input from the input “in” is put on the carrier fc of a predetermined channel and transmitted via the antenna X.

[0010] Next, the receiving block B passes through a demultiplexing circuit 1 to a required frequency band (fa = 254 MH in this case) demultiplexed from the signal supplied from the antenna X.
(a frequency band centered at z) is input. The receiving block B includes an RF (radio frequency) amplifier circuit 2
By mixing the bandpass filter 3 and the first local frequency fb supplied from the first local oscillation circuit 4 via the buffer amplifier 5 with the received signal, the first intermediate frequency of the difference between the two frequencies is obtained as a beat. A first mixing circuit (mixer circuit) 6A, an IF (intermediate frequency) band-pass filter 7 of a crystal filter, an IF amplifying circuit 8,
A second mixing circuit 10 that mixes the second local frequency supplied from the local oscillation circuit 9 and the first intermediate frequency to obtain a second intermediate frequency having a difference between the two frequencies as a beat;
A relay circuit 11 composed of an IF band-pass filter or an IF amplifier circuit of a ceramic filter; a detection demodulation circuit 12 for extracting an audio signal from the second intermediate frequency; An output stage circuit 13 composed of a decompression circuit for restoring the converted waveform and an output amplifier circuit 14 are connected in sequence. An audio signal is extracted from a carrier centered on fa received by the antenna X via these circuits. In addition,
t1 is a signal receiving terminal, t2 and t3 are channel switching block connection terminals, t4 is a receiving block output terminal, t5 is a power supply terminal (Vcc), and t6 is a common terminal (GRD).

The mixer circuit 6A of the present invention comprises an NPN transistor Q1, resistors R0, R1 to R3, R6, and capacitors C2, C3. According to FIG. 1, a mixer circuit 6A has a signal input terminal 61 connected to the base of a transistor Q1, a collector connected to a power supply terminal t5 via a resistor R0, and an emitter connected to a resistor R3 and a capacitor C2. It is connected to a common terminal t6 via a parallel circuit. A resistor R1 is connected between the base and the collector of the transistor Q1, and a resistor R2 is connected between the base of the transistor Q1 and the common terminal 2.
Further, the collector of the transistor Q1 and the signal output terminal 62
A resistor R6 is connected between them, and a capacitor C5 is connected between the signal output terminal 62 and the common terminal t6. Here, the resistor R0 is constituted by a mixer bias circuit in which the tuning circuit LC is omitted, and is formed so as to obtain impedance matching between the resistor R6 and the capacitor C5. In addition, the selectivity Q is set so as to satisfy the characteristics of the crystal filter XF1 which functions equivalently to the tuning circuit LC of the IF bandpass filter 7 in consideration of the circuit at the subsequent stage.

On the other hand, the IF band pass filter 7 takes in the signal output from the collector of the transistor Q1 to the crystal filter XF1 via the resistor R4 and the signal output terminal 62. 8 is connected. The output side of the resistor R5 is connected to the common terminal 2 via the capacitor C4.

In the mixer circuit 6A of FIG. 1, the power supply voltage Vc is applied between the power supply terminal t5 and the common terminal t6.
When a high frequency signal (RF signal) in which two frequencies are superimposed and mixed is input to the signal input terminal 61 in a state where the signal c is applied, that is, the reception signal fa transmitted via the antenna X and the first signal When the first local frequency fb supplied through the local oscillation circuit 4 is mixed and input, the transistor Q1 is turned on, impedance matching is performed by the resistors R0 and R6 and the capacitor C5, and both frequencies fa and fb are adjusted. The first intermediate frequency IF (for example, 2
1.7 MHz) and is sent to the next stage crystal filter XF1. Further, the quality of the characteristic is determined by the selectivity Q. When the selectivity Q increases, only the signal component is amplified and the other components are attenuated. Therefore, it is usually necessary to design the Q value to be high. At this time, the resistance R0,
R6 and capacitor C5 increase the selectivity Q of the IF
The circuit including the band-pass filter 7 is set so that impedance matching can be achieved. The crystal filter XF1 is a high-pass filter that passes a high frequency of 10.7 MHZ or higher, and is configured to select only a target frequency and not pass other frequencies. Is output to an amplifying transistor (not shown) of the IF amplifying circuit 8 at the next stage and is amplified.
It is configured to transmit the signal to the detection and demodulation circuit 12 at the subsequent stage.

The channel switching block C supplies a carrier frequency to a modulation circuit A4 of the transmission block A via a low-pass filter C2 at the time of transmission by a PLL circuit (phase lock loop) C1. Feedback is provided at the output of unit A5, thereby controlling the carrier frequency. At the time of reception, the first local frequency is supplied to the mixing circuit 6A via the low-pass filter C3, the transmission circuit 4, and the buffer amplifier 5, and the result is fed back at the output of the buffer amplifier 5, whereby the first local frequency is fed back.
It is configured to control the local frequency.

In such a transmission and reception system, each of the transmission block A and the reception block B and the antenna X
Is inserted into the receiving block B, or conversely, the signal fc output from the transmitting block A is mixed into the receiving block B.
a is suppressed from being mixed into the transmission block A,
A transmission / reception system with an improved N ratio is realized.

[0016]

[Effects of the Invention] As is clear from the above description, the present invention provides a mixer circuit in which a tuning circuit consisting of a tuning coil and a capacitor is eliminated, thereby reducing the cost by reducing the number of components and reducing the time required to receive a large input signal. It has the advantage of preventing the deterioration of the distortion rate with the improvement of the selectivity, and has the practical advantage of being a circuit suitable for a cordless telephone device because it can be reduced in size and weight.

[Brief description of the drawings]

FIG. 1 is a block diagram of a transmission / reception system including a circuit configuration diagram of a mixer circuit showing an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating an example of a conventional mixer circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Demultiplexing circuit 2 RF amplifier circuit 3 RF bandpass filter 4 1st local oscillation circuit 5 Buffer amplifier 6, 6A mixing circuit (mixer circuit) 7 IF bandpass filter 8 IF amplification circuit 9 2nd local oscillation circuit 10 2nd mixing Circuit 11 Relay circuit 12 Detection and demodulation circuit 13 Output stage circuit 14 Output amplification circuit 61 Signal input terminal 62 Signal output terminal A Transmission block B Reception block C Channel switching block t1 Signal reception terminal t2, t3 Channel switching block connection terminal t4 Reception block output Terminal t5 Power supply terminal (Vcc) t6 Common terminal (GND) Q1 NPN transistor R0 to R6 Resistance C1 to C5 Capacitor LC Tuning circuit CF1 Filter XF1 Crystal filter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/24-7/26 102 H04Q 7/00-7/38 H04B 1/26 H04M 1/02 H03D 7 / 12

Claims (1)

(57) [Scope of request for utility model registration] 1. A reception signal mixing circuit in a transmission / reception system for a cordless telephone device, wherein two high frequency signals of a reception signal fa and a local oscillation frequency fb of a required frequency band input via an antenna are mixed and superimposed and input. A signal input terminal, a NPN transistor having a base connected to the signal input terminal, a first resistor connected between a base and a collector of the NPN transistor, and a connection between a base and a common terminal of the NPN transistor. A second resistor, an impedance matching resistor connected between a collector of the NPN transistor and a power supply terminal, a third resistor inserted and connected between a collector of the NPN transistor and a signal output terminal, A first capacitor connected between the emitter of the NPN transistor and the common terminal; And a fourth resistor, and a second capacitor connected between the signal output terminal and a common terminal. The reception signal fa and the local oscillation frequency fb are mixed to extract a predetermined intermediate frequency. A reception signal mixing circuit configured to pass through a next-stage crystal filter via a signal output terminal, and then transmit to a subsequent detection circuit.