Indexed on: 02 Oct '14Published on: 02 Oct '14Published in: Analog Integrated Circuits and Signal Processing
A novel chopper indirect current feedback instrument amplifier (IA) is presented in this paper. Normally, low frequency signal is choppered to high frequency and then fed into an IA’s first amplification stage with low pass frequency response. While the signal is amplified, the offset and 1/f noise of the first stage are also enlarged. This leads to large ripple at IA’s final output. A bandpass amplifier taking use of active inductor is designed as the first stage of the chopper amplifier. It amplifies the high frequency signal and suppresses the offset and the low frequency noise at the same time. The ripple at the IA’s output is reduced. The IA comprises of a bandpass input stage and a folded cascode output stage. The second modulator is placed at the drains of the input transistors of the cascode amplifier. The offsets of those transistors which are between the bandpass amplifier and the second modulator are reduced by a ripple reduction loop. A verification circuit is designed in 0.18 μm CMOS technology. The measurement results show that the IA has a gain of 40 dB and its bandwidth is 7.1 kHz. The input referred noise is 74 nV/vHz and the input referred residual offset is 3 μV. Its common mode rejection ratio is over 130 dB. The core circuit occupies 0.16 mm2 chip area and consumes 30 μA from a 2.6 V power supply.