A 24.88 nV/\(\surd\)Hz Wheatstone Bridge Readout Integrated Circuit with Chopper-Stabilized Multipath Operational Amplifier  
[PERSON]  
1 Department of Electronics Engineering, Chungnam National University, Daejeon 34134, Korea; [EMAIL_ADDRESS] (K.H. ); [EMAIL_ADDRESS] (H.K. ); [PERSON]L_ADDRESS] (J.K.); [EMAIL_ADDRESS] (D.Y. ); [EMAIL_ADDRESS] (H.H. ); [EMAIL_ADDRESS] (Y.K.) [PERSON]  
1 Department of Electronics Engineering, Chungnam National University, Daejeon 34134, Korea; [EMAIL_ADDRESS] (K.H. ); [EMAIL_ADDRESS] (H.K. ); jk [EMAIL_ADDRESS] (J.K.); [EMAIL_ADDRESS] (D.Y. ); [EMAIL_ADDRESS] (H.H. ); [EMAIL_ADDRESS] (Y.K.) [PERSON]  
2 Department of Mechanical and Aerospace Engineering, Seoul National University, Seoul 08826, Korea; [EMAIL_ADDRESS] 2  
[PERSON]  
1 Department of Electronics Engineering, Chungnam National University, Daejeon 34134, Korea; [EMAIL_ADDRESS] (K.H. ); [EMAIL_ADDRESS] (H.K. ); [PERSON]L_ADDRESS] (J.K.); [EMAIL_ADDRESS] (D.Y. ); [EMAIL_ADDRESS] (H.H. ); [EMAIL_ADDRESS] (Y.K.) Received: 2 December 2019; Accepted: 3 January 2020; Published: 5 January 2020  
[PERSON] Abstract  
This paper proposes a low noise readout integrated circuit (IC) with a chopper-stabilized multipath operational amplifier suitable for a Wheatstone bridge sensor. The input voltage of the readout IC changes due to a change in input resistance, and is efficiently amplified using a three-operational amplifier instrumentation amplifier (IA) structure with high input impedance and adjustable gain. Furthermore, a chopper-stabilized multipath structure is applied to the operational amplifier, and a ripple reduction loop (RRL) in the low frequency path (LFP) is employed to attenuate the ripple generated by the chopper stabilization technique. A 12-bit successive approximation register (SAR) analog-to-digital converter (ADC) is employed to convert the output voltage of the three-operational amplifier IA into digital code. The Wheatstone bridge readout IC is manufactured using a standard 0.18 \(\upmu\)m complementary metal-oxide-semiconductor (CMOS) technology, drawing 833 \(\upmu\)A current from a 1.8 V supply. The input range and the input referred noise are \(\pm\)20 mV and 24.88 nV/\(\surd\)Hz, respectively. chopper-stabilized; multipath operational amplifier; Wheatstone bridge sensor; instrumentation amplifier (IA); ripple reduction loop (RRL)
The Wheatstone bridge readout integration circuits (ICs) primarily employ two conversion techniques [11]. The first is a voltage-to-frequency converter that converts analog signals into the frequency domain [15; 16; 17]. This scheme is simple in structure, but consumes considerable power and has a slow conversion rate over a wide operating range [18]. The other technique is a voltage-to-digital converter that converts analog signals into digital signals [19; 20]. The instrumentation amplifier (IA) is implemented to amplify small input signals, and an analog-to-digital converter (ADC) is required to convert the amplified signals to digital signals. Generally, the voltage-to-digital converter is more popular because of the well-established precision IA and ADC techniques. In the voltage-to-digital conversion, the IA is one of the key building blocks. A precision IA with low offset and low input referred noise is required because the offset and the input referred noise of the IA can generate a nonlinear output [21]. Various techniques have been implemented for precision IAs, such as autozeroing and chopping, to secure microvolt offset levels [22; 23; 24; 25; 26]. The autozeroing technique alleviates the offset and the flicker noise by sampling the offset and the low frequency flicker noise in the autozero capacitor in phase 1 (\(\Phi\)1) and subtracting this information from the output voltage in phase 2 (\(\Phi\)2). However, this technique generates switching noise due to sampling, and augments base band noise because of noise folding [27].