A transimpedance amplifier using a widely tunable PVT-independent pseudo-resistor for high-performance current sensing applications

Abstract

In this paper, we present a pseudo-resistor-based transimpedance amplifier (TIA) whose transimpedance value is PVT-independent and continuously tuneable over a wide range. The nonlinearity of the pseudo-resistors is mitigated by connecting a large number of elements in series and the effect of process variations on the pseudo-resistor is canceled by a biasing network based on a pseudo current mirror. The design is also first order temperature compensated exploiting the PTAT behavior of the proposed pseudo-resistor and using a PTAT current reference for its biasing. The proposed architecture is verified using a prototype manufactured in a 0.18 μm CMOS SOI technology. In this prototype, the transimpedance can be adjusted between approximately 1MΩ and 1 GΩ. The achievable bandwidth varies inversely proportional with the transimpedance value from around 7 kHz for a value of 1 GΩ up to an opamp-limited maximum of 2 MHz. In the white region, the input referred noise is equal to that of a TIA using an equivalent ohmic resistor. A minimum value of 5 fA/√Hz is achieved for a transimpedance of 1 GΩ. Over a temperature range from -40 °C to 125 °C, the transimpedance varies less than 10% for 1MΩ. The TIA occupies a chip area of 0.07 mm 2 . At room temperature, the power consumption is 9.5 mW from a single 1.8 V supply of which the pseudo-resistor consumes 0.2 mW.