JP3298237B2 - High frequency local oscillator 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 high-frequency local oscillation circuit, and more particularly to a high-frequency local oscillation circuit suitable for use in a high-frequency circuit of a digital car telephone or a digital portable telephone.

[0002]

2. Description of the Related Art Conventionally, a high-frequency local oscillation circuit as shown in FIG. In FIG. 5, the high-frequency local oscillation circuit includes a local oscillator for transmission 11, a band-pass filter 2, a buffer amplifier 6, a mixer for reception 7, and a band-pass filter 8, and the band-pass filter 2 is connected to the quadrature modulator 1. It is connected. In this oscillation circuit, a local oscillation frequency signal generated from a local oscillator 11 is applied to a bandpass filter 2.
, The reception band noise is attenuated by the band-pass filter 2 and then input to the quadrature modulator 1 as a transmission local oscillation frequency signal, and as a reception first local oscillation frequency signal. The data is input to the buffer amplifier 6.

[0003]

However, in the above-mentioned conventional high-frequency local oscillation circuit, since the local oscillation frequency signal output from the oscillator 11 is directly generated by the synthesizer, the sideband wave output from the quadrature modulator 1 is generated. Is a signal having a frequency very close to the carrier frequency of the synthesizer, and there is a problem that a transmitted modulated wave goes around the synthesizer during transmission and a beat is generated. Examples of this type of circuit include Japanese Patent Application Laid-Open Nos. 62-219886, 59-44129, and 58-21353.
No. 5 publication.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a high-frequency local oscillation circuit capable of suppressing occurrence of a beat.

[0005]

In order to achieve the above object, the present invention provides a first local oscillator for generating a first local oscillation frequency signal, and a second local oscillator having a frequency different from that of the first local oscillation frequency signal. A second local oscillator for generating a frequency signal, and one local oscillator of the local oscillation frequency signal upon reception
Oscillation frequency signal only mixing the first local oscillation frequency signal at the time of transmission output as to input the first local oscillation frequency <br/> speed signal reception and the second local oscillation frequency signal transmission modulated wave signal output A high-frequency local oscillator circuit comprising a transmitting mixer for performing the above-mentioned operation and a filter for passing a signal of only a specific component of the output signal of the transmitting mixer.

[0006]

Therefore, according to the present invention, the transmission modulation wave signal is generated by mixing the first local oscillation frequency signal and the second local oscillation frequency signal, so that the transmission modulation wave is kept away from the local oscillation frequency of the synthesizer. And the occurrence of beats can be suppressed. That, fTX a transmission modulation wave, the local oscillation frequency of the synthesizer fC, the second station oscillation frequency is f2 for reception, keep away fTX = fC + f2, and the local oscillation frequency of the synthesizer from frequency only transmission modulation wave fTX of f2 Can be. Furthermore, the first local oscillation frequency <br/> number received so generated is not an issue of beat, using a local oscillation frequency of the direct synthesizer to improve reception band noise, the first station oscillation signal upon reception Since only the first local oscillation frequency is input and used as the first local oscillation frequency for reception, the transmission modulation wave of the signal output from the mixer for transmission at this time can be the same frequency as the first local oscillation frequency for reception. , Filters can be used in common.

[0007]

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, a high-frequency local oscillator circuit of a digital car telephone comprises a quadrature modulator 1, a band-pass filter 2, a mixer 3, a first local oscillator 4, a second local oscillator 5 for reception,
It comprises a buffer amplifier 6, a first mixer for reception 7, a band-pass filter 8, a first intermediate amplifier 9 for reception, and a second mixer 10 for reception.

The first local oscillator 4 is configured to generate a first local oscillation frequency signal generated by a synthesizer, and the first local oscillation frequency signal (fC) is input to the mixer 3. A second local oscillation frequency signal (f2) is input from the oscillator 5 to the mixer 3. As shown in FIG. 2, the mixer 3 includes resistors R1 to R3, capacitors C1 to C5, inductances L1 to L4, and a mixing element 3A. The terminal A is connected to the oscillator 4, and the terminal B is connected to the oscillator 5. , Terminal C is connected to the bandpass filter 2, and terminal D is connected to the power supply. Further, the resistance R
A switch E is connected to both ends of 2. The switch E is turned on at the time of reception to close the contact, and turned off at the time of transmission to open the contact. That is, only the local oscillation frequency signal from the oscillator 4 is input during reception, the first local oscillation frequency signal and the second local oscillation frequency signal are input during transmission, and the input signals are mixed and transmitted. Output as a modulated wave signal.

The band-pass filter 2 has an attenuation characteristic as shown in FIG. 3, receives the transmission modulated wave signal from the mixer 3, and converts the signal of the input signal into a specific component only. It is made to pass.

Here, assuming that the transmission modulation wave is fTX, the local oscillation frequency of the synthesizer is fC, and the second local oscillation frequency for reception is f2, the transmission modulation wave fTX can be expressed by the following equation (1).

F TX = f C + f 2 (1) where f TX = 950 MHz, f C = 820.45 MHz, f 2
= 129.55 MHz.

On the other hand, when the switch E is turned on at the time of reception, the reception first local oscillation frequency fL0 is expressed by the following equation (2).

FL0 = fC '(2) Here, fL0 = fC' = 950 MHz. in this case,
From the expressions (1) and (2), the transmission modulation wave fTX is expressed by the following expression (3).

F TX = f L0 (3) The transmission modulated wave signal passed through the band-pass filter 2 is input to the quadrature modulator 1 and the buffer amplifier 6. The quadrature modulator 1 has characteristics as shown in FIG. 4, and the quadrature modulator 1 outputs a transmission modulation wave signal.

On the other hand, the transmission modulated wave signal input to the buffer amplifier 6 is input to the mixer 7 as a first local oscillation frequency signal for reception, and is mixed with the reception signal by the mixer 7 to be mixed with the first intermediate frequency signal for reception. Is input to the bandpass filter 8. Only a signal of a specific component among the signals input to the band-pass filter 8 is input to the first intermediate amplifier 7 for reception, amplified and then input to the second mixer 10 for reception. In the mixer 10, the signal from the intermediate amplifier 9 and the second local oscillation frequency signal from the oscillator 5 are mixed, and the mixed signal is output as the second intermediate frequency signal for reception.

As described above, according to the present embodiment, the second local oscillator that generates the first local oscillation frequency generated by the synthesizer and the transmission modulation wave output from the quadrature modulator 1 from the oscillator 5.
Since it is set apart by the oscillation frequency, the occurrence of beats can be suppressed. Further, the switch E of the mixer 3 is turned on at the time of reception, turned off at the time of transmission, and at the time of reception, only the first local oscillation frequency signal from the oscillator 4 is output as a transmission modulation wave signal. One local oscillation frequency can be the same frequency. Further, since the band-pass filter 2 is provided at the output of the mixer 3, the reception band noise and the transmission spurious can be attenuated in common by the same band-pass filter 2.

[0017]

As apparent from the above embodiment, the present invention mixes the first local oscillation frequency signal and the second local oscillation frequency signal during transmission to generate a transmission modulated wave signal. Therefore, the local oscillation frequency due to the generation of the transmission modulation wave and the synthesizer can be kept away, and the occurrence of a beat can be suppressed. Furthermore, since the time of reception so that only output as the transmission modulation wave signal one signal of the two local oscillator frequency <br/> speed signal, receiving local onset and transmission modulation wave
The vibration frequencies can be the same frequency.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a high-frequency local oscillation circuit showing one embodiment of the present invention.

FIG. 2 is a specific circuit configuration diagram of a mixer.

FIG. 3 is a characteristic diagram of a band-pass filter.

FIG. 4 is a characteristic diagram of a quadrature modulator.

FIG. 5 is a schematic block diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quadrature modulator 2 Bandpass filter 3 Mixer 4 1st local oscillator 5 2nd local oscillator 6 Buffer amplifier 7 1st mixer for reception 8 Bandpass filter 9 1st intermediate amplifier for reception 10 2nd mixer for reception

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-237342 (JP, A) JP-A-5-206917 (JP, A) JP-A-4-213205 (JP, A) JP-A-7- 74632 (JP, A) JP-A-6-224958 (JP, A) JP-A-2-7624 (JP, A) JP-A-5-65138 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03B 21/00 H04B 1/00-1/53 H04L 27/00-27/30

Claims (1)

(57) [Claims] A first local oscillation frequency signal generating means for generating a first local oscillation frequency signal;
Local oscillator and the second local oscillator and one of the local of the local oscillation frequency signal upon receiving the first local oscillation frequency signal to generate a different second local oscillation frequency signal having a frequency
Oscillation frequency signal only mixing the first local oscillation frequency signal at the time of transmission output as to input the first local oscillation frequency <br/> speed signal reception and the second local oscillation frequency signal transmission modulated wave signal output A high-frequency local oscillator circuit, comprising: a transmission mixer that performs transmission; and a filter that passes a signal of only a specific component among output signals of the transmission mixer.