| 摘要 |
<p>A signal comparison circuit compares the frequency and phase of a first input signal with the frequency and phase of a second input signal in an error-free manner. A first flip-flop (28) triggered by the first input signal produces negative pulses, under the control of a NAND latch (32). A second flip-flop (30) is triggered by the second input signal to produce negative pulses, under control of the same NAND latch. The first and second input signals are each delayed, and the delayed input signals are respectively used to trigger slave flip-flops (34 and 36). The outputs of the slave flip-flops control the state of a NOR latch (381. The NAND latch indicates which of the two input signals leads the other in phase, while the NOR latch indicates which of the input signals has a higher frequency than the other. The outputs of the NAND and NOR latches are decoded and provide a control voltage to a voltage-controlled oscillator to vary the frequency of the oscillator in accordance with a reference frequency.</p> |
