| 摘要 |
<p>A multi-stage logarithmic converter of the 'successive-detection' or 'progressive-compression' type including means providing an accurate, temperature-stabilized logarithmic transfer function. The gain stages are DC-coupled throughout, though each also employs a demodulator comprising a full-wave rectifier, allowing operation in both baseband and demodulating modes. The signal path is differential and is balanced, including the demodulators. Each gain stage is based on a differential amplifier, or 'long-tail pair' operated in an open-loop mode and biased by a tail current generator which supplies a tail current that is both proportional to absolute temperature and compensated automatically for effects of finite transistor beta and base and emitter resistances. The demodulators are biased by a very low offset voltage which also is proportional to absolute temperature. The log intercept is temperature-stabilized by either employing a PTAT attenuator ahead of the complete amplification system or by introducing at the output node (a current summing junction) a current which varies with temperature in such a way as to offset intercept movement which otherwise would be generated.</p> |
