锁相环 Phase Locked Loop
The phase locked loop contains two phase comparators, a voltage-controlled oscillator VCO, source follower, and zener diode. The comparators have two common signal inputs, PCA can be used directly coupled to large voltage signals, or indirectly coupled with a series capacitor to small voltage signals. The self-bias circuit adjusts small voltage signals in the linear region of the amplifier. Phase comparator 1 an exclusive OR gate provides a digital error signal PC1, and maintains 90 phase shift at the center frequency between PCA signals both at 50% duty cycle. Phase comparator 2 with leading edge sensing logic provides digital error signals, PC2 and LD, and maintains a 0 phase shift between PCA signals duty cycle is immaterial. The linear VCO produces an output signal VCO whose frequency is determined by the voltage of input VCO and the capacitor and resistors connected to pins C1, R1, and R2. The source-follower output SF with an external resistor is used where the VCO signal is needed but no loading can be tolerated. The inhibit input Inh, when high, disables the VCO and source follower to minimize standby power consumption. The zener diode can be used to assist in power supply regulation. Applications include FM and FSK modulation and demodulation, frequency synthesis and multiplication, frequency discrimination, tone decoding, data synchronization and conditioning, voltage-to-frequency conversion and motor speed control.
Features
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