FTA-T-21 Operational Amplifier

The FTA-T-21 pin 2 is falsely disconnected from its pin 3, which means that there is no current output from pin 2 of the FTA-T-21, so there is I2=I1. In other words, we get a constant current output of 0.5mA at C. Since the voltage signal at the ends of the Pt resistance temperature sensor measured by the FTA-T-21 is weak, this voltage must be amplified by an amplifier circuit before A/D conversion.

FTA-T-21 input signal between 50mV ~ 70mV, the A/D conversion voltage range of 0V ~ 2.5V, after calculation, the amplifier circuit amplification of 35 times or so can meet the requirements of A/D conversion. Ordinary operational amplifiers are generally more than hundreds of microvolts of input offset voltage, the temperature coefficient of the offset voltage is more than a few microvolts above zero.

The FTA-T-21 input offset voltage can be zeroed, but its drift is difficult to eliminate. The chopper-stabilised zero-type operational amplifier FTA-T-21 provides an inexpensive solution to the problem of micro-signal amplification. The chopper-stabilised zero operation gives the FTA-T-21 excellent DC characteristics, with an out-of-phase voltage of 0.5 μV (typical) to 1 μV (maximum); an input out-of-phase drift voltage of 0.003 μV/°C (typical), and a long-term out-of-phase voltage drift of 0.003 μV/month [3][8]. After calculation, the performance parameters of the FTA-T-21 can meet the requirements of the measurement accuracy of this system, so the op-amp in the amplifier circuit of this system adopts the TLC2652.