## 1 Introduction  
The resistive micro-electro-mechanical system (MEMS) sensors are widely used to detect information, such as pressure, temperature, humidity, and biological signals [1; 2; 3; 4]. Resistive MEMS sensors have advantages, such as low price, high linearity, and simple structure. Resistive MEMS sensors are mainly implemented with the Wheatstone bridge structure, which converts the resistance change into a voltage change with several mV. The converted voltage is too small to process resistive sensor applications. For this reason, a readout integrated circuit (ROIC), for resistive sensor signal processing, is required. The amplification stage in the ROIC is usually implemented with an instrumentation amplifier (IA). For high precision signal processing, the IA should have low-input noise and high-input impedance. Since the input signal has only a few of mV, low-frequency noise, such as flicker noise, can distort the baseline of input signal. Additionally, with the low-input impedance of IA, the effect of the mismatch with sensor electrode can be large, resulting in high-input offset and low CMRR of IA. In addition, for portable battery-powered systems, low-power implementation is required for longer operating hours. While maintaining low-power consumption, the performances for high, open-loop gain, fast slew rate, large-output swing, and low-noise characteristics should be achieved for high precision signal equation. The folded cascode (FC) topology is widely used for gain stage in the amplifier, as shown in Figure 1a. However, as shown in Figure 1a, the role of transistors _MN_1 and _MN_2 is only limited to providing the small-signal input current to the folding node. To overcome this inefficiency, a modified FC was presented, replacing the current source with active current mirrors, as shown in Figure 1b, called recycling folded cascode (RFC) [5]. Many studies have been also reported using RFC structures to enhance power efficiency [6; 7; 8]. The current mirror with a 1:\(K\) ratio increases transconductance, and the cross-over connections keeps the small-signal currents, added at the sources of \(M\)N5 and \(M\)N6, in phase. The resulting transconductance and gain bandwidth (GBW) of the RFC are:  
\[G_{mRFC}=g_{mPM1a}(1+K) \tag{1}\]  
\[GBW_{RFC}=\frac{g_{mMP1a}(1+K)}{2\pi C_{L}} \tag{2}\]  
With \(g_{mPM1a}\), the transconductance of the transistor \(MP1a\) and \(C_{L}\) the load capacitor is shown at the output node, OUT. For the same area and power consumption, the RFC delivers wider bandwidth, higher gain, and higher slew rate than the FC topology. For resistive-bridge sensor readout, the resistance-to-voltage conversion has an advantage of relatively large dynamic range; however, nonlinear outputs, due to the effects of noise and the nonzero offset by the readout circuit, can occur. To minimize those non-linearity error components, a precise sensor readout circuit, with low noise and offset, is required. The chopper stabilization scheme can reduce low-frequency noises, achieving the required low-noise specification [9]. Figure 2 shows the well-known chopping principle, with chopped amplifier and its ideal time domain waveforms. The input voltage in the DC band, \(V_{in}\), is modulated by a chopper CH1, with clock frequency \(f_{ch}\), and it is converted to a modulated AC signal. Next, the modulated AC signal and input offset are amplified together with amplifier gain, \(A\). Then the output chopper, CH2, demodulates the amplified AC modulated signal back to DC signal. The offset to the odd harmonics of \(f_{ch}\), modulated by the CH2, can be filtered out after passing the LPF. Thus, the thermal-noise limited signal-to-noise ratio (SNR) can be achieved. Figure 1: (**a**) conventional folded cascode; (**b**) recycling folded cascode. In this paper, we propose a low-noise, low-power, and high-input impedance readout IC for resistive microsensors. To overcome the power-noise tradeoff, the chopper-stabilized, current-feedback instrumentation amplifier (CFIA), with RFC topology, is proposed.