mikelm
G1 is a voltage controlled current source, in this circuit it is standing in for the entire differential transistor front end of the amplifier – the differential voltage at the +/- terminals of G1 controls the current source output
the G1 circuit function is an idealization of the diff front end with current mirror, the gain of 0.01 A/V corresponds to 1/(100 Ohm), or about the same Gm as a diff pair with 100 Ohm emitter degeneration resistors
i'm using G1 to save the 4-5 Qs that make up a the front end because orcad demo is limited to 10 transistors - also it lets you concentrate on the VAS + Output properties and sims faster
it turns out that real diff pairs are so good that replacing them with the ideal G1 block doesn't change circuit operation much - the main limitation here is that the Super Pair input impedance is so high that the ouput impedance of the current mirrored diff pair @ > 1 MOhm and < 5 pF would lower circuit gain a little
G1 is a voltage controlled current source, in this circuit it is standing in for the entire differential transistor front end of the amplifier – the differential voltage at the +/- terminals of G1 controls the current source output
the G1 circuit function is an idealization of the diff front end with current mirror, the gain of 0.01 A/V corresponds to 1/(100 Ohm), or about the same Gm as a diff pair with 100 Ohm emitter degeneration resistors
i'm using G1 to save the 4-5 Qs that make up a the front end because orcad demo is limited to 10 transistors - also it lets you concentrate on the VAS + Output properties and sims faster
it turns out that real diff pairs are so good that replacing them with the ideal G1 block doesn't change circuit operation much - the main limitation here is that the Super Pair input impedance is so high that the ouput impedance of the current mirrored diff pair @ > 1 MOhm and < 5 pF would lower circuit gain a little
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