IC2a operates as the converter, while IC2b provides a degree of temperature compensation. In this circuit only two of the individual transistors are used, and no connections are made to the other devices. having their emitters connected together).
Macspice all voltages negative plus#
IC2 is a CA3046 transistor array, which consists of three individual transistors plus two others connected as a long-tailed pair (i.e. Having tried a variety of configurations, this one seems to give reasonably accurate and stable results without the need for any “difficult to obtain” components. The circuit must therefore include temperature compensation to avoid the need for very frequent readjustment to correct tuning drift. What does complicate things is that the voltage across a forward biased silicon diode varies significantly with changes in temperature, and diodes are often used as electronic temperature sensors. Although this characteristic is only maintained over certain limits, in this application there is no need to exceed these limits as only a modest ,range of output currents is involved (no more than a range of about 100 to 1). This converter circuit, in common with most other types of logarithmic amplifier, relies for its operation on the fact that the current through a forward biased silicon diode rises exponentially with linear increments the input voltage. But here it is a very strange set up to me. Here is the text that describes the circuit (Copied from the book):įrom every log opamp I have seen the diode is part of the feedback of the opamp.
My question is can anyone please explain to me what the diode does and why it seems to be shorted out across the 741 opamp. The text that describes the circuit is as follows. Hi The following diagram is a circuit from a synthesizer book by R.A Penfold.
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