## 3 Measurement Results  
The die photograph of the fabricated low-noise chopper operational amplifier is shown in Figure 4. The prototype chopper operational amplifier is fabricated by a 0.18-\(\upmu\)m CMOS process. The prototype chip has an amplifier-active area of 0.213 mm\({}^{2}\). The measured total current consumption of the chopper operational amplifier is 278.3 \(\upmu\)A, with a power supply of 3.3 V.  
The measurement environment of the prototype chopper operational amplifier is shown in Figure 5. The prototype amplifier is tested on a designed printed circuit board (PCB) by a chip-on-board process (COB) connected by wire bonding. The DC power supply supplies 3.3 V of power, and the gate of the lateral PNP input stage is biased with 3.3 V. The waveform generator generates input pulses and sinusoidal signals for amplifier configuration tests. The dynamic signal analyzer is used for spectrum analysis, and a digital oscilloscope is used for signal acquisition. The open-loop gain measurement result of the proposed chopper operational amplifier is shown in Figure 6. The measured average open-loop gain is 115 dB, and the measured gain bandwidth (GBW) of the chopper operational amplifier is 2.30 MHz, with a chopper frequency of 250 kHz. Figure 4: Die photograph of prototype chopper operational amplifier. Figure 5: Measurement environment of prototype chopper operational amplifier. Figure 3: (**a**) Before base current cancellation operation; (**b**) operation of proposed BJT current mirror base current cancellation. The measurement results of the input-referred noise are shown in Figure 7. The measured input-referred noise with the chopper off is shown in Figure 7a. The measured input-referred noise, with the chopper off at 1 Hz, is 36.3 nV/Hz. The measured input-referred noise level with the chopper off is 7.31 nV/Hz, with a noise-integrated bandwidth of 0.5 to 800 Hz. The measured input-referred noise with the chopper on, with a chopper frequency of 250 kHz, is shown in Figure 7b. The measured input-referred noise, with the chopper on at 1 Hz, is 29 nV/Hz. The measured input-referred noise level with the chopper on is 5.43 nV/Hz, with a noise-integrated bandwidth of 0.5 to 800 Hz. The measurement results show that the implementation of the BJT input stage can achieve a low-noise characteristic compared to previous works [13, 14, 22]. The measurement results, with the chopper off and on, show that the overall noise characteristic can be improved by using the chopper. The measurement results of the input base current, with a chopper frequency of 250 kHz, are shown in Figure 8. The measured input base current without the proposed base current cancellation is 156.263 nA, which is shown in Figure 8a. The measured input base current with the proposed base current cancellation is 67.971 nA, which is shown in Figure 8b. The measurement results show that the proposed base current cancellation does not completely cancel the input base current; however, the input base current can be compensated by reducing the input base current by more than half of that before the base current cancellation operation. The common mode rejection ratio (CMRR) measurement result of the proposed chopper operational amplifier is shown in Figure 9. The measured average CMRR is 115.1 dB, and CMRR at 60 Hz is 90.9 dB with a chopper frequency of 250 kHz. The power supply rejection ratio (PSRR) measurement result of the proposed chopper operational amplifier is shown in Figure 10. The measured average PSRR is 66.6 dB, and PSRR at 60 Hz is 68.3 dB with a chopper frequency of 250 kHz. Figure 5.0 Open-loop gain measurement result of the proposed chopper operational amplifier. Figure 5.1 (**a**) Measured input-referred noise with the chopper off; (**b**) Measured input-referred noise with the chopper on. The slew rate measurement result is shown in Figure 5.2 The slew rate measurement proceeded with a buffer configuration, with a loading output load of 10 k\(\Omega\) and 120 pF.