EMRFD Message Archive 4607

4607 2010-04-29 07:34:39 Nick Kennedy Squarer circuit for power indication Message Date From Subject 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. http://pages.suddenlink.net/wa5bdu/squarer.htm 73- Nick, WA5BDU [Non-text portions of this message have been removed] 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