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Generation of Voltage Controlled Signal for Phase Locked Loop
3.3 Generation of Voltage Controlled Signal
3.3.1 Amplifier
A differential amplifier and low pass filter convert the phase detectors' signals to a variable voltage control signal for the VCO current
source. The differential amplifier increases the phase lock loop signal with a gain of -1.8. While the low pass filter integrates this
amplified signal causing a variable output at was calculated from 3.05V to 6.00V. A schematic of the amplifier and filter is shown in Figure 3.3.1.
3.3.2 Implementation of Low Pass Filter
A low pass filter is used to perform an integrator function at the free running frequency of the phase lock loop, 10KHz. The LM565 has an internal
resistor, R12, of 3.6KΩ for the use of the low pass filter. We choose to use a 0.1μF capacitor with resistor R12 because it provided a breakpoint
frequency at 442Hz, giving us a wide frequency integration range, and availability of this value of capacitance. The following is the transfer
function and bode plot for the low pass filter.
fc = 1 / (2Π R12 C2) = 442Hz
Figure 3.3.2 Bode plot of the transfer function for the low pass filter.
3.3.3 Output Results of the Amplifier and Filter
The input of the amplifier and filter provides a variable voltage from a measured value of 3.48V to 5.74V to the VCO
depending on the signal that comes from the phase detector.
Electrical Engineering lab key words: Voltage generation, amplifier, bjt, differential amp, PLL, phase lock
loop, loop filter, LF, VCO, signal generator, amplification, frequency detector, PFD, stages, feedback signal,
Analog Devices, Maxim IC, National Semiconductor, vendors, telecommunications, power, supply voltage, output
characteristics, low pass filter, clipping, frequency range, bandwidth, roll off, cutoff frequency, BJT, break
frequency, circuit transfer function, VCO, output stage, simulation, PSPICE. |
