Noise Performance of a Regulated Cascode Transimpedance Amplifier for Radiation Detectors

Abstract

A low noise transimpedance amplifier (TIA) is used in radiation detectors to transform the current pulse produced by a photo-sensitive device into an output voltage pulse with a specified amplitude and shape. We consider here the specifications of a PET (positron emission tomography) system. We review the traditional approach, feedback TIA, using an operational amplifier with feedback, and we investigate two alternative circuits: the common-gate TIA, and the regulated cascode TIA. We derive the transimpedance function (the poles of which determine the pulse shaping); we identify the transistor in each circuit that has the dominant noise source, and we obtain closed-form equations for the rms output noise voltage.We find that the common-gate TIA has high noise, but the regulated cascode TIA has the same dominant noise contribution as the feedback TIA, if the same maximum transconductance value is considered. A circuit prototype of a regulated cascode TIA is designed in a 0.35 m CMOS technology, to validate the theoretical results by simulation and by measurement.

Comments on “Noise Performance of a Regulated Cascode Transimpedance Amplifier for Radiation Detectors”

“…The transfer function (see (8), (15b), (15c) or (22) in [1]) (1) can be rewritten following the notation used in [2] and [3]: (2) where , and and is the input referred noise voltage source of the opamp. Note that and are the pole-frequency and pole-Q of the realized transfer function.…”

“…The rms output amplifier noise can be obtained from (2) using (3) as (4) which can be seen to be same as (10) in [1].…”

“…In this comment, we point out that closed-form expressions for estimating the noise transfer function of a general biquadratic transfer function are available in literature [2], [3]. A straightforward application of these to the desired transfer functions for estimating the output noise is shown to yield closed form expression for output noise for the circuits considered in [1]. The contribution of the noise of the resistor is also compared with that due to opamp noise…”

“…Recently, Oliveira et al [1] have derived closed form expressions for the rms output noise voltage of several types of transimpedance amplifiers for radiation detectors. They consider the effect of finite bandwidth of the opamp which results in a second-order noise transfer function corresponding to the input referred noise of the opamp.…”

“…They consider the effect of finite bandwidth of the opamp which results in a second-order noise transfer function corresponding to the input referred noise of the opamp. In Appendix A in [1], they have presented a complete derivation of the output noise of a system with two real poles and one zero, which was used to compare the various transimpedance amplifier topologies. In this comment, we point out that closed-form expressions for estimating the noise transfer function of a general biquadratic transfer function are available in literature [2], [3].…”