| 摘要 |
PURPOSE:To obtain a phase comparison circuit without DC offset, by connecting a current switch which is conductive only when the 1st input signal is at a specific polarity, to a differential pair transistor(TR) which performs differential operation in response to the 2nd input signal. CONSTITUTION:A power supply voltage VB is applied to each base of differential pair TRs Q1 and Q2 of common emitter connection via a resistor R1 and R2. A TRQ3 as a current switch is connected to a common emitter connecting point of the TRs Q1 and Q2. The 1st input signal is applied to the base of the TRQ3 via a capacitor C1. The 2nd input signal is applied to the base of the TRQ2 via a capacitor C2. A current mirror circuit consisting of TRs Q4 and Q5 is connected to the collector of the TRs Q1 and Q2. Through this constitution, if the input signals are missing or discontinuous, the TRQ3 is turned off and a phase comparison output without DC offset can be obtained. |
