To achieve the detection of extremely weak signals from pyroelectric infrared detectors and to meet the demands of high-sensitivity applications, this paper proposes a dual-capacitor transimpedance amplifier (CTIA) readout structure featuring a variable array size. And a bandgap reference and a low dropout regulator (LDO) were designed as the bias circuit to provide voltage bias, in order to meet the requirements of low noise, low power consumption, large dynamic range and portability. The circuit is designed in TSMC 0.18μm 1P6M CMOS process under a 3.3V supply. For the layout implementation, advanced techniques, including dummy structures and guard rings, are employed to improve device matching, overall layout symmetry, as well as the noise immunity and electrical stability of the analog circuitry.