| 摘要 |
Temperature and technology-independent selt-calibrating monolithic logarithmic amplifier systems that use integrated cascades of current-summing or voltage-summing differential-limiter gain stages are disclosed. Each stage is trimmed and stabilizedby a respective bias replicator cell and a current mirror cell. The bias replicator provides a bias current control signal in response to a change in a given difference between currents in a differential pair of amplifiers controlled by a predetermined differential calibration voltage. The differential pair is identical to a differential pair in the limiter amplifier. The differential calibration voltage E lin is well-within the linear portion of the amplifier's transfer curve during operation, so that the proportional relation between Ek and Elin, which is the same as that between the given difference between currents and the correct bias current value IB, remains constant throughout. The bias replicator signal then varies the input bias current of the limiter amplifier to correcto for temperature-related and technology-related bias-current errors. The current mirror uses an op amp connected to a calibration voltage equal to the correct limit voltage of the amplifier to detect a change from that voltage across avariable resistance to cancel that change, and to matching variable load resistances in the gain cell to correct for temperature-related and technology-related load-resistance errors.
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