Amplifier circuit with transistors - has two operational amplifiers with feedback and connection through transistor to third and fourth amplifiers

摘要

The system measures without the use of a reference voltage the voltage across a current carrying resistor. It has two operational amplifiers with full feed-back, working as impedance transformers. Each amplifier input is connected to one of the resistor terminals, and their outputs to a further operational amplifier. A first transistor (T1) base-emitter path is inserted into the first amplifier (18) feed-back circuit. Its emitter is connected through a resistor (R1) to the second amplifier (20) output, and collector through a resistor (R2) to a voltage source (+U), and to the input of the further amplifier (22), whose output is connected to a transistor (T2). Its collector is connected through a resistor (R4) to the reference potential, and emitter through resistor (R3) to the terminal (+U).