THE USE OF A 1.2 V-SUPPLY CMOS AMPLIFIER AS A FRONT END FOR INTEGRATED SENSOR APPLICATIONS

摘要

In portable electronic systems both low voltage and low power operation is of fundamental importance. Low supply voltages are important because it is desirable to use as few batteries as possible for reducing size and weight; low power consumption is necessary to obtain a high battery lifetime. A building block in low-voltage low-power analog design is the operational amplifier (op-amp). In sensor applications, the op-amp is connected in typical configurations, such as : differential amplifiers, oscillators, to be utilized as sensor front-end circuits. In these applications, the op-amp fundamental characteristics are : low offset, low noise, complete input and output dynamic range, constant-transconductance over the input common mode voltage (to ensure a power-efficient frequency compensation) and reduced sensitivity to temperature and supply variations. A novel low-voltage (1.2 V) low-power (0.26 mW) CMOS op-amp has been considered. It has a very efficient output stage, able to drive loading resistance as low as 500 Ω, with 2V/us slew rate and 380 ns settling time. The DC gain is 80 dB for 1KΩ and 124 dB for 1 MΩ load. The gain bandwidth is 2 MHz. CMRR and PSRR values are greater than 63 dB. The op-amp has low noise (the equivalent input voltage noise is about 1.5 nV/(Hz)1/2) and low systematic offset (less than 0. 1mV). The total harmonic distortion is -93 dB. The circuit, designed in a standard O.5μm technology, has rail-to-rail input and output stages and constant transconductance (within 15% of variation) over the input common mode signal. A very reduced dependence on both temperature and supply variations has been noticed. Some examples of the op-amp in low-voltage (1.2V) fully integratable sensor interface configurations are reported, concerning capacitive, resistive and temperature sensors.