gillbert cell mixer bjt
pls can anyone tell me how to analyse gillbert cell mixer(bjt)
how to decide the values of resistance ,capaci&inductance
u can say that gilbert cell has three parts , the transconductor , the switching and the load
the transconductor is the lower pair , which u inject the RF to them , the quad , used as the switching , the output used the resistance or inductance to get the output
usually the gain of the mixer depends on the gm of the tarnsconductor , and the switching , is it a sinusoid or square wave switching , also the gain depends on the load , and also the output frequency spectrum depends on the load is it tuned or resistive for wide band operation
khouly
MIXER OPERATION
The RF signal is applied to the transistors M2 & M3
which perform a voltage to current conversion. For correct
operation these devices should not be driven into
saturation and therefore, signals considerably less than
the 1dB compression point should be used. Performance
can be improved by adding degeneration resistors, on
the source terminals of M2 & M3.
MOSFets M4 to M7 form a multiplication function,
multiplying the linear RF signal current from M2 and
M3 with the LO signal applied across M4 to M7 which
provide the switching function.
M2 and M3 provide +/- RF current and M4 & M7
switch between them to provide the RF signal or the
inverted RF signal to the left hand load. M5 & M7
switch between them for the right hand load.
The two load resistors form a current to voltage transformation
giving differential output IF signals.
for analysis replace mosfets by BJT
how to bias the BJT? is it using a special biasing method or just normal biasing (active mode)?