I have a circuit which converts it's input to the log of it's bipolar peak. It uses Vbe matched small signal transistors, thermally bonded, as the logging element. If kept within a thermal cocoon, it can exhibit an accuracy of within 1dB over an 80dB range. This was something I built long ago as a noise meter without range switching; the meter face spans an 80dB range which can be switched to give RMS, peak, or average responding. I can prepare a schematic if anyone's interested. Michael At 07:23 PM 8/11/99 -0400, you wrote: >Regarding the discussion of the use of non-linear amplifiers for >compression of seismic output. > >I have tried a circuit which uses a feed-back amplifier with multiple >diodes and resistors in the feedback path. If germanium diodes are >used, the output can be switched smoothly at each .5 volt point to any >gain desired. It can be used for both posative and negative signals. >In a feedback instrument this cannot be in the feedback to the >instrument, otherwise the system stability is affected. It must be in a >separate output channel. > >The circuit is any opamp with the primary feedback resistor having >direct connection and chosen to give the sensitivity needed for small >signals. In parallel with this is a pair of diodes in parallel back to >back which are in series with a smaller resistor. This smaller resistor >defines a smaller gain when the diodes conduct in either direction. The >diode pairs can be continued with ever smaller resistors to define other >switching points and scale factors. The output is a smooth curve in >both polarities. > >The probem is that the diode resistance change is not sharp, so that the >output curves must be converted by use of a curve approximation in a >calculation or table look-up if precision is desired. > >Has anyone tried something similar? > >George Harris > > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@.............. with the body of the >message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>