Too large load capacitance, too low transistor fT, emitter/collector resistor too high?My experiments with simple transistors show that depended on the frequency there are amplitude variations and large phase errors.
Notice at your simulation phases are not exactly 180 degrees out of phase. This is what I experience myself. Also the phase moves a bit as the frequency changes (1-30MHz). Why is this happening and can it be corrected?A test shows the effect of transistor choice. BFR92A is SMD equivalent of popular BFR90 5GHz transistor.
The circuit needs to be modified if you want to drive a lower load impedance. It might be easier to use additional common collector buffer amplifiers in this case.
View attachment 168044
Please read the text comment in the schematic. Phase error with general purpose transistor 2N2222 is 17.5 degree, with BFR92A it's only 1.5 degree.
Main causes are transistor capacitances (mainly Ccb) and limited transit frequency fT.
Yes, it should work too. A word of warning, these GHz transistors are likely to self-oscillate in your circuit at several 100 MHz, a base series resistor of 50 to 100 ohms often helps to supress oscillations.
Yes, it should work too. A word of warning, these GHz transistors are likely to self-oscillate in your circuit at several 100 MHz, a base series resistor of 50 to 100 ohms often helps to supress oscillations.
I cannot simulate it.An integrated Gilbert cell, as the cheap NE612, would provide a stable and accurate phase shift over the entire frequency range.
FvM, see this modification I did in your circuit. I have decreased the input signal as well as the emitter resistor.A test shows the effect of transistor choice. BFR92A is SMD equivalent of popular BFR90 5GHz transistor.
The circuit needs to be modified if you want to drive a lower load impedance. It might be easier to use additional common collector buffer amplifiers in this case.
View attachment 168044
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