Measurement of the power spectral density of noise produced by a large integrated feedback resistor for charge-sensitive preamplifiers

Charge-sensitive preamplifiers (CSP) require high-valued feedback resistors as continuous-time reset devices: higher resistance values correspond to lower current noise and better spectroscopic performances. Designing integrated multi-channel CSP such resistors are generally left as external components or substituted with active transconductors. The former are bulky and not adequate for situations where a high degree of integration is required, the latter generally suffer from linearity and noise problems. A possible solution could be the use of large integrated polysilicon resistors. These ones, however, suffer from a very high distributed capacitive coupling to bulk, which tends to turn such devices into transmission lines. Simple resistor models are no longer adequate to describe both the impedance and the noise generators of such integrated resistors. A closed-form model was developed which describes the current noise produced by a resistance with distributed capacitance. A 100 Mohm integrated polysilicon resistor was realized and the power spectral density of noise produced by this device has been measured connecting it as a feedback resistor to a low-noise charge-sensitive preamplifier.