1. Common-emitter amplifier circuits with a low input impedance and a high output impedance can amplify both current and voltage.
2. Common base amplifier circuits with very low input impedance and very high output impedance can amplify the voltage and cannot amplify current.
3. Common collector amplifier circuits with very high input impedance and very low output impedance can amplify the current and cannot amplify voltage. Because of the relationship between the input and output impedance, it is often used for voltage following and power amplification.
The integrated operational amplifier matches three circuits above to make the amplifier's characteristics closer to the ideal condition.
4. Gain bandwidth
Gain bandwidth can be roughly considered as the amplifier's amplification performance, or as GBW which is determined when it is manufactured. GBW represents the ability of high frequency amplification of an operational amplifier, through which we can estimate the high frequency performance. Estimation is as follows:
GBW= A frequency x The maximum magnification that can be reached at the frequency.
5. Problem of the feedback resistance in parallel with the capacitance
This is a kind of method to compensate the operational amplifiers
ahead. If the operational amplifier has a pole in the transmission, it can easily trigger oscillations, or distort the gain spectrum. In order to eliminate this pole, it is necessary to be in parallel with the capacitance. However, it will result that the system stability is improved and the transmission characteristic of the system is lost, which can make the amplifier's high frequency amplification ability drop rapidly.
6. Problem of operational amplifiers to be power amplifiers
It is OK to take operational amplifiers as power amplifiers. We can use a small operational amplifier to put the output end of the operational amplifier and the power amplifier in parallel ( take balance current measures), or buy a large operational amplifier, such as PA02, whose output current can have several amperes. The power of 3MHZ is not very high, such as BUF602 BUF634, but they need a voltage amplifier to provide the driving voltage.