An Auto-Zero Stabilized Voltage Buffer with a Trimmed Input Current of 0.2pA

This paper presents an input-current trimming scheme for auto-zero amplifiers. Since their input current is mainly due to charge injection, the scheme operates by trimming the clock swing, and hence the charge injection, of two dummy input switches. At room temperature, the trimming scheme reduces the maximum input current of an auto-zero stabilized voltage buffer from 1pA to 0.2pA (13 samples) over its full input voltage range (0 to 1.3V). This increases to 0.4pA over temperature (0 to 85°C), which is well below the leakage of typical ESD diodes, and is the lowest input current ever reported for an auto-zero amplifier.