Hello everyone. I would like to know more about the transistor long tailed pair. I have seen various versions of this building block and most of them include a current mirror constant current source that replaces the emitter resistor. However, I have seen one that has two constant current sources: one in the collector and one in the emitter. Why is this useful and does it affect the quality of amplification?
Constant current sources have the disadvantage imposed by transistor output characteristics. This is NEVER a series of horizontal lines but always slanting lines with a positive gradient. Therefore, given a current source's bias is contant, the output current is a function of the voltage experienced by the collector juntion. If you want to limit unwanted current dependency, you can use a cascode to remove the effect of the voltage acting on the collector.
In your post, I am getting the impression you are describing how constant current sources are implemented within ICs. Yes, current mirrors are used. I do not know how the circuit you are describing is precisely, but two transistors in a current mirror can be used to supply double the normal current mirror's set current. The reason for this stems from the fact, the collector currents are almost 'independent' of collector voltage.
In your post, I am getting the impression you are describing how constant current sources are implemented within ICs. Yes, current mirrors are used. I do not know how the circuit you are describing is precisely, but two transistors in a current mirror can be used to supply double the normal current mirror's set current. The reason for this stems from the fact, the collector currents are almost 'independent' of collector voltage.
A cascode on the output of a current source will drastically reduce the effect of the collector voltage on the current source's set current.
I simulated this on LTSpice with very encouraging results. A current source can also be constructed using an op-amp and a transistor.
Any more non-descriptive grave-yard like names for technical terms?
I simulated this on LTSpice with very encouraging results. A current source can also be constructed using an op-amp and a transistor.
Any more non-descriptive grave-yard like names for technical terms?