ACTIVE MULTIPLIER

HI,
I AM A MEMBER OF THE TEAM INVOLVE IN DESIGN AND DEVELOPMENT OF TELEMETRY AND TELECOMMAND RECEIVERS, IN THAT CONNECTION I HAD DESIGNED AN ACTIVE TRIPLER ( HEMT BASED) WITH THE CONVERSION LOSS OF 4dB RESPECTIVELY. ONCE THE CIRCUIT IS TESTED IN NORMAL ROOM TEMPERATURE (25°C), I KEPT IT IN A CHAMBER FOR HOT AND COLD CYCLES ( -30°C TO 65°C),DURING COLD THE BIAS CURRENT ( VGS=-0.7V,VDS=0.9V AND ID=0.00123mA AT NORMAL ROOM TEMPERATURE) DECREASES TO 0.00011mA AND ONCE THE RF IS SUPPLIED THE CURRENT SWINGS TO 7.1mA RESPECTIVELY ON THE OTHER HAND DURING HOT CYCLE THE BIAS CURRENT (WITHOUT RF) INCREASED TO 0.01123mA BUT ONCE THE RF IS SUBJECTED THE CURRENT RISES TO 5.3mA ONLY, NOW MY QUERY IS WHY IN HOT INSPITE OF DC CURRENT IS MORE THAN THAT OF COLD THE CURRENT IS LESS ONCE THE RF IS SUBJECTED? OTHER OBSERVATION IS THAT IN COLD RF POWER AT THIRD HARMONICS IS LESS AS COMPARED TO HOT, OPPOSITE TO THAT OF LINEAR AMPLIFIERS WHERE THE POWER IN COLD INCREASES AS COMPARED TO HOT!

There are a couple ways to make a tripler:
1) antiparallel shottky diodes to generate the 3rd harmonic, and linear amplify after that
2) non-linear element (varactor or step recovery diode) and present the correct impedances/filtering to the element terminals to force it to triple
3) other nonlinear methods, like photonic mach-zender modulators, digital gates with waveshapers at the output, etc.
4) take a transistor, bias it up so it is highly non-linear, and present the impedances/filtering to the gate and drain to optimize the generation of the harmonic of interest.

It sounds like you are using #4. So, how are you biasing it up so that over all temperatures it is operating at the same non-linear operating point? Vp or Vbe in transistors is going to vary wildly over temperature, so fixed bias is not going to work too well.

Rich

Active Frequency multiplier would have been more appropriate topic for this query.

As multiplier in analog electronics means mixer .

Can anybody explain in case of HEMT/MESFET which are biased deep in nonlinear region(for multiplier action), how the bias point shifts(or vary) as the circuit experience extreme cold and hot temperatures ?

As there are two ways to bias such a circuit 1) near saturation region2) near pinchoff.