Winning the battle for low gain error and high CMRR — A current sense amplifier with trimmable gain resistors

State-of-the-art CSAs employ precision, albeit expensive, thin-film resistors to achieve current sense amplifiers (CSA) with low gain error and high common mode rejection ratio (CMRR). This paper presents a CSA architecture which uses standard, low cost polyslicon resistors in conjunction with a resistor trimming method to obtain similar performance. Binary weighted resistors are enabled by blowing metal fuses in order to adjust both the gain error and the total CMRR of the CSA. Measurements are performed on over 200 chips. The maximum gain error is reduced 20 times, from 1% to 0.05%. Also, the total CMRR of the CSA is increased from a minimum of 65 dB to a lower limit of 100 dB, over a common-mode voltage range up to 48 V.