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Circuit explanation
of PLL synthesizing oscillator(2)

PLL synthesizer oscillator (MC145163) Reference frequency The circuit this time makes an oscillation frequency 10.24MHz. Dividing ratio of the reference frequency To change the frequency of the output by the dividing ratio of the comparison frequency in the 10KHz unit, the dividing ratio is fixing on 1024 at the circuit this time. Dividing ratio of the comparison frequency Because the 144-MHz bandwidth of the amateur radio is 2MHz(144.0MHz to 146.0MHz) in Japan, it makes the output frequency of the PLL 133.3MHz to 135.3MHz. (Frequency with the low of 10.7MHz) The comparison frequency which is inputted to MC145163 is mixed with 119.3MHz by SN16913 and becomes 14MHz to 16MHz. Because the phase comparison frequency is 10KHz, the dividing range of the comparative divider becomes 1400 to 1600. The BCD specification value of 103 is fixed on 1 and the BCD specification value of 102 is made to be able to choose 4 or 5. The BCD specification value of 102 becomes 0100 or 0101 when it is displayed by bits. The bit of 20 is made to be able to be changed into 0 or 1. 101 and 100 specify 0 to 9 by the binary-coded decimal code. The frequency of 200 channels can be specified by the 10KHz unit by above dividing ratio specification. Voltage controlled oscillator ( VCO ) The oscillation frequency of the voltage controlled oscillator is controlled by the output of the PLL synthesizer and does the oscillation operation of the stable frequency. As the oscillation circuit, it is using Colpitts LC oscillation circuit. C3 and C4 become the capacitors of the Colpitts circuit for the voltage division. The oscillation frequency is changed by the capacitance of C5, D1 and D2. D1 and D2 are the variable capacitance diode (the varicap diode). The capacitance of the diode changes when gaining opposite direction voltage. The capacitance becomes small when making opposite direction voltage high. Two diodes are using for expanding the adjustment range of the frequency. The signal for the control which is output from the charge pump of MC145163 is a pulse signal. A pulse signal is changed into the voltage change of the direct current through the filter by R4, R5, R6 and C6. Double balanced mixer (SN16913) Top view It mixes two input frequencies and it outputs the frequency of the difference. This time, it mixes 133.3MHz - 135.3MHz of frequency of the VCO and 119.3MHz of the outside oscillator and it is outputting 14MHz - 16MHz. When mixing, added frequency (252.6MHz - 254.6MHz) is output too. Because it isn't possible to handle a 200MHz frequency in MC145163, 14MHz - 16MHz are used as the input. The rating The maximun rating Item Symbol Rated value Unit Power supply voltage VCC 16.5 V Input voltage Vi 7.0 V The electric characteristic Item Symbol Min Typ Max Unit Power supply voltage VCC 4.0 15.0 V Electric current consumption ICC 15.0 mA RF input voltage 300 mVp-p Local input voltage 300 mVp-p Output buffer To prevent from an influence from the external circuit over the oscillation, an output buffer is provided. Two the same circuits are preparatory as the output buffer. One is used for the transmitter and the other one is used for the receiver. The FET transistor is using for the output buffer. The FET is an electric Field Effect-type Transistor. The output current (the drain electric current) can be controlled at the voltage which is gained by the input (the gate). Usual transistor controls an output current in the electric current which flows through the base. In case of the FET, because to pass an input electric current isn't necessary, it is possible to compose with the simple circuit.