Abstract: An improved integrated circuit oscillator adapted for crystal-controlled applications eliminates the need for capacitors and duty cycle control circuitry by using a cascaded pair of push-pull complementary transistor amplifier stages, a clipping-type automatic amplitude control circuit, and a resonant feed back path between the two amplifier stages. In an illustrative embodiment, floating bias voltages are established by a chain of diodes, with several bias currents set with respect to the chain current by emitter area relationships. Square-wave output is provided by a flip-flop connected to push-up and pull-down output circuits.

Abstract: A common control digital echo suppressor is disclosed which is configurable as full or split selectively on a channel-by-channel basis. Improved break-in and reduced hangover are provided by an arrangement for approximating the anticipated echo signals more accurately and by a wait-window technique to better distinguish between impulse noise and speech for break-in. The echo signal arrangement accurately approximates anticipated echo during both the rising and falling portions of speech signals. The wait-window technique provides for substantially instantaneous break-in, then a short wait period for impulse noise to subside, followed by a speech sampling window. If outgoing signals are detected during the window, suppression removal goes into a full break-in state. Otherwise, suppression is reinserted at the end of the window.

Abstract: The detection sensitivity and noise rejection of an arrangement for detecting speech in the presence of noise is improved by accumulating the weighted differences between input signal samples and their short-term running average. The detector thus tracks ambient noise, providing an adaptive detection threshold such that detection sensitivity is increased in low noise environments without excessive false operation on high level noise. The peak average attained during an interval of speech is used to provide variable hangover upon cessation of speech, yielding greater hangover for weak talkers than for loud talkers. In an illustrative embodiment of the speech detector used in a speech interpolation system, protection is afforded also against false transmission path operation due to detection of speech echo.