O
Oliver Friedrich
Guest
Hallo experts,
I've designed two different amplifiers for the region around 1MHz. Both
of them should have a gain of 35dB@1MHz an input impedance of ca 50-100
Ohm.
After designing I did DC, AC and Transient analysis using OrCAD PSpice.
Both of them worked well, and the gains, biases did behave exactly as
designed (Great, if simulations match to theory ;-)).
Now I've built these two amps on a proper layout. Amp 1 behaves exactly
like simulation (even greater when reality mathes simulation ;-)), the
biases matched the simulation down to a few millivolts and uamps, gain
like simulated, current consumption like simulated, impedance like
simulated...
Amp 2 matches the simulation in all DC biases, but lacks almost 13dB of
gain and behaves different in its frequency response.
We've checked the assembly over and over again, there shouldn't be any
wrong capacitors or inductors on the board. I suspected these cause these
are the only one which can be wrong without affecting the DC-behaviour.
1) What else could be the cause for this discrepancy?
2) The transistors used are BC847C, BC857C, BFS20 and BF824. Does anyone
know the models for these, are they correct at 1MHz?
Schematics can be provided on demand.
Thank you
Oliver Friedrich
I've designed two different amplifiers for the region around 1MHz. Both
of them should have a gain of 35dB@1MHz an input impedance of ca 50-100
Ohm.
After designing I did DC, AC and Transient analysis using OrCAD PSpice.
Both of them worked well, and the gains, biases did behave exactly as
designed (Great, if simulations match to theory ;-)).
Now I've built these two amps on a proper layout. Amp 1 behaves exactly
like simulation (even greater when reality mathes simulation ;-)), the
biases matched the simulation down to a few millivolts and uamps, gain
like simulated, current consumption like simulated, impedance like
simulated...
Amp 2 matches the simulation in all DC biases, but lacks almost 13dB of
gain and behaves different in its frequency response.
We've checked the assembly over and over again, there shouldn't be any
wrong capacitors or inductors on the board. I suspected these cause these
are the only one which can be wrong without affecting the DC-behaviour.
1) What else could be the cause for this discrepancy?
2) The transistors used are BC847C, BC857C, BFS20 and BF824. Does anyone
know the models for these, are they correct at 1MHz?
Schematics can be provided on demand.
Thank you
Oliver Friedrich
480)460-2350 | |