ethan
Member level 3
op amp theory
on page 155, figure 5.3.18 in Huijsing's opamp theory and design,
He said, for this general-amplification feedforward biased class-AB output stage,
1. "Q3, Q5, Q4, Q6 form a positive coupling loop with a current gain of slightly lower than1, which keeps this loop stable."
I think this is a current loop, but I don't how to explain it as a positive loop with current gain less than one. Any help?
2. "The currents which are lost in the diode connected biasing transistors Q3 and Q4 are collected by the emitters of Q5 and Q6 respectively, and are returned as driving current to the complementary side."
how to understand this?
3. "All input current which is not used to drive one output transistor is used to drive the other. So, the gain decrease due to the class-AB biasing circuit is eliminated. In fact, the positive loop-gain coupling is a way to implement a class-AB bias circuit with high input impedance."
And how to understand this also?
Appreciate your help.
on page 155, figure 5.3.18 in Huijsing's opamp theory and design,
He said, for this general-amplification feedforward biased class-AB output stage,
1. "Q3, Q5, Q4, Q6 form a positive coupling loop with a current gain of slightly lower than1, which keeps this loop stable."
I think this is a current loop, but I don't how to explain it as a positive loop with current gain less than one. Any help?
2. "The currents which are lost in the diode connected biasing transistors Q3 and Q4 are collected by the emitters of Q5 and Q6 respectively, and are returned as driving current to the complementary side."
how to understand this?
3. "All input current which is not used to drive one output transistor is used to drive the other. So, the gain decrease due to the class-AB biasing circuit is eliminated. In fact, the positive loop-gain coupling is a way to implement a class-AB bias circuit with high input impedance."
And how to understand this also?
Appreciate your help.