| 摘要 |
A downhole digital power amplifier comprises a device which, through digital means, provides a sinusoidal, variable frequency, variable power and variably phase-shift modulated output for the transmission of data from a downhole sensor arrangement to an uphole receiver. Selection and variation of frequency, power and modulation are made through digital inputs. The device provides these functions at extra low frequencies (ELF) low-to-high power output, and varying phase-shift keying. The downhole digital power amplifier (68) comprises, in a preferred embodiment, an input shift register (81) for receiving a digital bit stream, a programmable frequency divider (82), a dead man timer circuit (84), a counter (86), a sync circuit (88), a PROM (90) (programmable read-only memory) for generating a digital sinusoidal output, a DAC (92) (digital-to-analog converter) for converting the digital sinusoidal output to an analog sinusoidal output, a power supply control circuit (94), an analog divider (96), and a conventional power amplifier (98). The dead man timer circuit detects normal operation and a fault condition, and controls the power supply control circuit to "power down" the amplifier when reception of a digital bit stream is not imminent during normal operation, and controls the power supply control circuit to periodically generate a "failure informant" message during a fault condition.
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