CMOS Impedance Analyzer for Nanosamples Investigation Operating up to 150 MHz With Sub-aF Resolution

This work addresses the emerging need for investigating micro- and nano-devices by performing Impedance Spectroscopy with high-sensitivity yet at high bandwidth. To this goal a new circuital architecture has been implemented that overcomes the limitations of the classic transimpedance topology of noise and maximum operating frequency trade-off as well as of input capacitance stability concerns. Thanks to a two channel modulation/amplification/demodulation structure embedded into a feedback loop, high loop gain at all the working frequencies is obtained. Implemented in 0.35 mu m CMOS, the IC works from 1 kHz up to 150 MHz, independently of the input capacitance value up to about 100 pF. The IC shows a resolution as good as 0.4 aF in the 100 kHz-150 MHz range (Vin = 1 V, BW = 50 Hz). The circuit directly provides two DC outputs proportional to the Real and Imaginary component of the DUT admittance so that no external lock-in structure or filter is required. The output bandwidth is adjustable from few tens of Hz up to 50 kHz, thus allowing both fast impedance tracking and high resolution impedance spectroscopy.