| 摘要 |
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, VP, and produces conditioned signal, VC. A magnitude of VC is proportional to an amplitude of VP offset by a negative DC voltage. A track and ramp circuit (30) receives VC and produces a tracking voltage, VT. A magnitude of VT is inversely proportional to the magnitude of VC when the track and ramp circuit is in a tracking mode. A controller (16) includes a clock that produces clock pulses, VCK and a divider (38) that divides the clock pulse frequency and produces a trigger pulse, VTRIG. A leading edge of the VTRIG pulse starts a counter (40) counting VCK pulses. The leading edge of an optically transmitted VTRIG pulse is applied to the latch circuit (32), which produces a ramp command voltage, VR. A high V R voltage places the track and ramp circuit (30) in a ramping mode and causes the magnitude of VT to decay at a constant rate. The latch circuit produces an echo pulse, VE, when VT decays to zero volts. An optically transmitted VE pulse is applied to the counter (40). A leading edge of the optically transmitted VE pulse stops the counter (40) from counting VCK pulses. The counter (40) produces an output signal, SOUT, having a value in the form of VCK pulses counted by the counter (40) during the elapsed time between the production of the VTRIG pulse and the receipt of the optically transmitted VE pulse. The SOUT value is proportional to the amplitude of VP.
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