EMRFD Message Archive 4607

Message Date From Subject
4607 2010-04-29 07:34:39 Nick Kennedy Squarer circuit for power indication
I was fascinated by a simple circuit in the Fall 2009 QRP Quarterly, taken
from KD1JV's web page. It's a simple circuit with some very complicated
theory behind it. I did some research on the translinear principle and
though I can't say I understood it in depth, it was interesting. Also
played with the circuit itself on LTSpice and then by building one on a
proto board.

My web site discusses some practical aspects of circuit sensitivity to
changing certain resistors and a general idea of how to scale the thing for
your meter and power measurement. Also links to a discussion of the theory
and to Steve Weber's page and his circuit.



Nick, WA5BDU

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4609 2010-04-29 15:18:58 victor Re: Squarer circuit for power indication
The operation of the circuit is not that complicated.
If we refer to the circuit diagram that you attached, when we increase Vin by a small step dVin, current Iy will increase by dIy = dVin/R1 .
Q1 and Q3 both have same operating points: same Iy and both have same Vbe=Vce so when Iy increases by dIy both Q1 and Q3 Vbe will increase by the same dVbe which means that Q3 emitter voltage will be more negative by 2*dVbe.
Q2 operating point does not change by the dVin jump because it receives its bias by R4 resistor, so its emitter voltage will not change. This means that the 2*dVbe negative jump at Q3 emitter will appear across base-emitter of Q4. Now we know that Ic of transistors change as exponent of its Vbe, so a jump of 2*dVbe