AlOA4

AlOA4 Phase Lock Loop 3 (PLL3) Up Converter,

Circuit Description

The function of AlOA4 is to mix 160 MHz with the output of AlOA5 (.15 to 6 MHz), up-converting that output by 160 MHz. The two frequencies are mixed together in a phase lock loop which has a closed loop bandwidth of approximately 10 kHz.

Frequency Multiplier x 1.6 @

The frequency multiplier generates 160 MHz from the 100 MHz at the input. U3 divides the input by 5 and produces harmonics of the resulting 20 MHz. The 160 MHz bandpass filter selects 160 MHz, which is then amplified by Q5 and buffered with a pad to -20 dBm. All three adjustments are set by peaking the 160 MHz signal.

160 to 166 MHz VCO @

The 160 to 166 MHz VCO uses Ql in a Colpitts configuration. Lll centers the frequency range of the VCO while CR3 is the varactor which tunes the oscillator. Q2 and Q4 are buffer amplifiers.

Mixer @

U7 is a double-balanced mixer which operates with about f7 dBm of LO power at 160 to

166 MHz and -20 dBm of RF signal power at 160 MHz. The desired output is the difference frequency which falls in the range between 150 kHz and 6 MHz.

IF Amplifier @

The output of the mixer U7 is filtered by an 8-section elliptic filter which must reject 14 to 20 MHz, and other higher frequencies. The filter output is amplified by Q3.

Loop Amplifier @

The phase detector outputs are connected to the differential inputs of U2. C9 and R16 provide ac feedback around U2 while dc feedback is provided by the entire phase lock loop. CR4 and CR5 lessen the charging time of C7 when the input frequency is changed abruptly. R14, R15, and C7 form an ac voltage divider which sets the loop bandwidth to about 10 kIIz. The output of the divider goes to the varactor in the oscillator and tunes the VCO. UlB prevents this tune voltage from latching at a positive value by sensing when the voltage goes above 0 V. When this occurs, the output of UlB pulls the tune voltage down to the proper lock range. R13 provides hysteresis to allow time for the loop to lock.

AlOA4 1