B
billcalley
- Jan 1, 1970
- 0
Hi All,
I'm having a very hard time understanding the full picture on
amplifier stability, even if I am an engineer. For instance, if we
select a transistor that is unconditionally stable at our frequency
band of interest -- let's say from 900MHz to 1000MHz -- but the
transistor is only conditionally stable at all other frequencies: So,
we bias, match, and resistively stabilize the transistor so that we
finally see, in the linear simulator, that K is greater than 1, and B1
is greater than 0. This should indicate that we now know that the
amplifier will not oscillate under any input/output impedance
conditions. But what happens when you place a filter at the input or
output port of our newly stabilized amplifier? Since the stopbands of
the filter are anything *but* 50 ohms when the amplifier is looking
out-of-band, wouldn't there still be a chance that this
"unconditionally stable" amplifier could oscillate, since it is only
based on a conditionally stable transistor?
Thanks!
-Bill
I'm having a very hard time understanding the full picture on
amplifier stability, even if I am an engineer. For instance, if we
select a transistor that is unconditionally stable at our frequency
band of interest -- let's say from 900MHz to 1000MHz -- but the
transistor is only conditionally stable at all other frequencies: So,
we bias, match, and resistively stabilize the transistor so that we
finally see, in the linear simulator, that K is greater than 1, and B1
is greater than 0. This should indicate that we now know that the
amplifier will not oscillate under any input/output impedance
conditions. But what happens when you place a filter at the input or
output port of our newly stabilized amplifier? Since the stopbands of
the filter are anything *but* 50 ohms when the amplifier is looking
out-of-band, wouldn't there still be a chance that this
"unconditionally stable" amplifier could oscillate, since it is only
based on a conditionally stable transistor?
Thanks!
-Bill