JPS5820489B2 - Local oscillation output circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a local oscillation output circuit used, for example, in a citizen's band transceiver.

According to the revised standards issued by the US Federal Communications Commission (FCC) in July 1976, 27 MHz band citizen band transceivers are subject to restrictions on spurious emissions during reception.

In addition, the standards for proximity spurious radiation during transmission have become more stringent.

Spurious radiation during reception can be reduced by reducing the output level of the local oscillator circuit, and this method is the most effective and reliable.

However, in a transceiver that uses a local oscillator circuit for both transmission and reception, the output of the local oscillator circuit is used as a local oscillator signal to generate transmission carrier power during transmission, so the local oscillator signal level must be set just enough to obtain the predetermined carrier power. Therefore, the local oscillation output level cannot be reduced very much.

Therefore, to reduce spurious radiation during reception,
It is necessary to switch the output level of the local oscillator circuit for transmission and reception.

It is easy to use a changeover switch or an electronic switch as a method for this changeover circuit, but the wiring to the switch terminal is very disadvantageous to spurious radiation, and the use of an electronic switch is For example, this requires a control circuit such as a switching transistor, which is disadvantageous in terms of cost, and at the same time, it may cause harmonic distortion in the local oscillation output during transmission, thereby worsening proximity spurious radiation during transmission.

□ This invention uses a very simple circuit configuration to improve proximity spurious radiation during transmission while supplying the local oscillation output level necessary to obtain a predetermined carrier power, and during reception, the local oscillation output level is sufficiently reduced to improve reception. The object of the present invention is to provide a local oscillation output circuit that can extremely reduce spurious radiation.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The figure is an electrical connection diagram showing an embodiment of the present invention.

In the figure, 10 is the generally known phase
-Lock -Loop (hereinafter referred to as PLL) frequency synthesizer with reference oscillator 112 phase detector 12° low-pass filter 13. Voltage controlled oscillator 14. and a programmable counter 15.

A channel selector 16 determines the frequency division ratio of the programmable counter 15.

The operation of PLL frequency synthesizer 10 will be described below.

The phase detector 12 compares the phases of the output of the reference oscillator 11 and the output of the programmable counter 15, and generates a voltage corresponding to the phase difference.

The output of the programmable counter 15 is applied to the voltage controlled oscillator 1 at a division ratio determined by the channel selector 16.
This is the frequency-divided output of 4.

A low-pass filter 13 integrates the output of the phase detector 12 and converts it into a DC voltage.

The voltage controlled oscillator 14 oscillates at a frequency proportional to the output voltage of the low pass filter 13.

If there is a phase difference between the output of the reference oscillator 11 and the output of the programmable counter 15, the output voltage of the low-pass filter 13 changes the frequency of the voltage-controlled oscillator 14 in a direction in which no phase difference occurs. When the phase difference disappears, the voltage is maintained and the voltage controlled oscillator 14 oscillates at a constant frequency.

Since the frequency of the voltage controlled oscillator 14 is determined by the frequency division ratio of the programmable counter 15, the frequency of the voltage controlled oscillator 14 can be changed by changing the frequency division ratio with the channel selector 16.

That is, the PLL frequency synthesizer 10 oscillates at a frequency corresponding to the channel of the channel selector 16.

The output of the PLL frequency synthesizer 10, that is, the local oscillation output, is passed through the capacitor 17 to the local oscillation output circuit 20.
is supplied to.

Local oscillation output circuit 20 includes a transistor 21, which is an example of a transistor circuit, and an output tuning circuit 24.

Output tuning circuit 24 includes a tuning transformer 24a and a capacitor 24b.

The base of transistor 21 is biased by resistors 22 and 23.

A tuning transformer 24a tuned around the local oscillation output frequency is connected to the collector of the transistor 21.

A parallel circuit of an emitter resistor 26 and an emitter bypass capacitor 27 is connected between the emitter of the transistor 21 and ground.

A bypass capacitor 28 is connected between the intermediate tap of the tuning transformer 24a and ground.

A power supply terminal 29 to which a bias voltage is supplied is connected to the center tap of the tuning transformer 24a.

The other terminal of the tuning transformer 24a and the transistor 2
A capacitor 25 for feeding back the output of the output tuning circuit 24 is connected between the base of the output tuning circuit 24 and the base of the output tuning circuit 24 .

The output of the local oscillation output circuit 20 configured in this manner is taken out from the secondary side of the tuning transformer 24a, and is passed through the capacitor 31 to the receiving mixer 33 and then to the capacitor 3.
2 to the transmit mixer 34.

In the local oscillation output circuit 20 configured as described above, at the time of transmission, the power supply voltage is applied to the intermediate tap point of the tuned transformer 24a, that is, the terminal 29, and the transistor 21 is biased through the resistor 22.23.
It works as a frequency selective amplification circuit tuned to the .

At this time, the capacitor 25 feeds back the output whose phase has been inverted by the tuning transformer 24a.

Therefore, it constitutes a negative feedback amplifier circuit, which has good stability and works as an amplifier circuit that generates little harmonic distortion.

Since an output with less harmonic distortion can be obtained in this way, the occurrence of proximity spurious during transmission, which is often caused by harmonic distortion, can be suppressed, and a transmission output with less proximity spurious radiation can be obtained.

Further, during reception, no voltage is applied to the terminal 29, and the transistor 21 is not biased.

Therefore, the capacitor 25 and the tuning transformer 24a function as a narrowband filter and have no amplification effect, and the output level of the local oscillation output is sufficiently lower than that during transmission, making it possible to extremely minimize spurious radiation from the chassis during reception. can.

In this circuit configuration, the power supply voltage applied to the terminal 29 during transmission only needs to lead to the power supply voltage that is switched between transmission and reception, which is very simple in terms of circuit configuration, and there is no need for a dedicated switching element, which is advantageous in terms of cost. be.

As described above, according to the present invention, spurious radiation during transmission and reception can be reliably reduced with an extremely inexpensive and simple circuit configuration, and a transceiver with extremely high performance can be provided.

[Brief explanation of the drawing]

The figure is an electrical connection diagram showing an embodiment of the present invention. In the figure, 10 is a PLL frequency synthesizer, 16 is a channel selector, 20 is a local oscillation output circuit, 29 is a power supply voltage terminal, 33 is a transmission mixer, 34 is a reception mixer,
17, 31 and 32 are capacitors.

Claims (1)

[Claims] 1. A local oscillation output circuit used in a transceiver capable of transmitting or receiving, comprising: an output tuning circuit; a power supply terminal provided in association with the output tuning circuit and to which a bias voltage is applied during transmission; a transistor circuit that selectively amplifies the tuning frequency of the output tuning circuit when a bias voltage is applied to the power supply terminal; and a transistor circuit that feeds back the output of the output tuning circuit as an input to the transistor circuit during the transmission. The transistor circuit and the capacitor work together as a negative feedback amplifier during transmission when a bias voltage is applied to the power supply terminal, and during reception when a bias voltage is not applied to the power supply terminal. The local oscillation output is specially designed so that the output level of the local oscillation output circuit is lower during reception than during transmission by the output tuning circuit and the capacitor working together as a narrow band filter. circuit.