Importance

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Abstract

An apparatus (10) for transmitting a patient physiological signal is provided. A converter (12) includes a front end circuit (28) that receives and conditions a patient physiological signal, V.sub.P, and produces conditioned signal, V.sub.C. A magnitude of V.sub.C is proportional to an amplitude of V.sub.P offset by a negative DC voltage. A track and ramp circuit (30) receives V.sub.C and produces a tracking voltage, V.sub.T. A magnitude of V.sub.T is inversely proportional to the magnitude of V.sub.C when the track and ramp circuit is in a tracking mode. A controller (16) includes a clock that produces clock pulses, V.sub.CK and a divider (38) that divides the clock pulse frequency and produces a trigger pulse, V.sub.TRIG. A leading edge of the V.sub.TRIG pulse starts a counter (40) counting V.sub.CK pulses. The leading edge of an optically transmitted V.sub.TRIG pulse is applied to the latch circuit (32), which produces a ramp command voltage, V.sub.R. A high V.sub. R voltage places the track and ramp circuit (30) in a ramping mode and causes the magnitude of V.sub.T to decay at a constant rate. The latch circuit produces an echo pulse, V.sub.E, when V.sub.T decays to zero volts. An optically transmitted V.sub.E pulse is applied to the counter (40). A leading edge of the optically transmitted V.sub.E pulse stops the counter (40) from counting V.sub.CK pulses. The counter (40) produces an output signal, S.sub.OUT, having a value in the form of V.sub.CK pulses counted by the counter (40) during the elapsed time between the production of the V.sub.TRIG pulse and the receipt of the optically transmitted V.sub.E pulse. The S.sub.OUT value is proportional to the amplitude of V.sub.P.

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First Claim