| 摘要 |
PURPOSE:To simplify the circuit constitution of a tone receiver which consists of a differential amplifier, band-pass filter, and comparator which detects an audio frequency sine-wave signal for test, and providing a confirmation signal generating circuit consisting of reverse parallel diodes and an integrating circuit. CONSTITUTION:A sine wave signal of about 1,000Hz sent out to a speech circuit is amplified by the differential amplifier AMP, passed through the band-pass filter BPF, and converted by the comparator COMP into a pulse signal, which is applied to the integrating circuit which consists of diodes D1 and D2, a resistance R7, and a capacitor C2. When the signal is a positive pulse, the capacitor C2 is charged through the diode D1. When it is a negative pulse, the diode D2 conducts, but the value of the resistance R7 is extremely large, so the discharge is extremely small. A transistor Q2 is turned on with the terminal voltage across the capacitor C2 to energize a relay RL2, thereby generating a signal for confirming the sine-wave signal of about 1,000Hz. |
