A 55-dB SNDR, 2.2-mW double chopper-stabilized analog front-end for a thermopile sensor

Abstract

A double chopper-stabilized analog front-end (DCS-AFE) circuit for a thermopile sensor is presented, which includes a closed-loop front-end amplifier and a 2nd-order 1 bit quantization sigma-delta modulator. The amplifier with a closed-loop structure ensures the gain stability against the temperature. Moreover, by adopting the chopper-stabilized technique both for the amplifier and 2nd-order 1-bit quantization sigma-delta modulator, the low-frequency 1/f noise and offset is reduced and high resolution is achieved. The AFE is implemented in the SMIC 0.18 m 1P6M CMOS process. The measurement results show that in a 3.3 V power supply, 1 Hz input frequency and 3KHz clock frequency, the peak signal-to-noise and distortion ratio (SNDR) is 55.4 dB, the effective number of bits (ENOB) is 8.92 bit, and in the range of -20 to 85 degrees, the detection resolution is 0.2 degree.

Chopping for over 50 MHz gain‐bandwidth product current sense amplifiers achieving input noise level of 8.5 nV/√Hz

“…However, the bandwidth was strictly limited by 200 Hz 10 . More recently, several very promising works have been published using more advanced semiconductor technologies and more complex design concepts in order to even further reduce input noise and offset, while also dealing with chopping‐related challenges 11–25 …”

“…As mentioned before, the basic principle of chopping is widely utilized for high‐precision operational amplifiers (opamps), especially for amplifying audio 23 and weak sensor signals, for example, in medical applications, 25 of a thermopile sensors, 18 or of a micro electro‐mechanical system (MEMS) sensors 16 . For these examples, chopping or chopper stabilization is very attractive, since, for example, bio‐signals or ambient‐sensor signals are typically weak and consist of very low frequencies.…”

“…10 More recently, several very promising works have been published using more advanced semiconductor technologies and more complex design concepts in order to even further reduce input noise and offset, while also dealing with chopping-related challenges. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In general, one typically distinguishes between (1) pure or classical chopping as employed in this work, which is partially extended to nested chopping using several interleaved choppers 3,26 ; (2) chopper stabilization, which is a multipath amplifier approach utilizing a main amplifier and a nulling amplifier 27 ; and (3) analogous auto zeroing, for example, using switched capacitors. Although the basic principle of the latter is different, it is still related to this topic, since the inputs are switched and input offset is reduced.…”