General Description: The AN7500FHQ is a single chip IC optimum for a 1.5 V headphone stereo system including pre-amp., power amp. and Dolby B type noise reduction circuit. Current consumption in a Dolby circuit off mode has been drastically reduced and an operating supply voltage has also been lowered to 0.98 V. Much fewer external components have been realized due to an integration of audio signal processing system into a single chip circuitry in a small outline package and space saving mounting of a set. Circuit Diagram Audio signal processing IC for 1.5 V headphone stereo
A retriggerable monostable multivibrator and a D flip-flop can form a simple, yet reliable frequency comparator that compares an input frequency with a predetermined reference. To determine whether an input frequency (f) falls between two known frequencies, f1 and f2, two one-shot/flip-flip combinations are used, as shown. Here both the one-shot and the flip-flop ICs are wired for positive-edge triggering. Each input pulse causes the monostable output to go high for the period of its preset timing interval. The flip-flop is triggered simultaneously, but its output is determined by the state of its D input at the time of trigger threshold. If the period of the input frequency is shorter than the preset timing of the monostable, a constant high level will be present at the D input, forcing the flip-flop’s Q output to remain high. If the input frequency period becomes greater than that of the monostable, the flip-flop’s Q output will go low. VR1, VR2, and C1, C2 determine the value of...