An integrated CMOS baseline restorer based on a switched current-conveyor

We present a fully integrated CMOS gated baseline restorer for shaper amplifiers with shaping times of up to 10 mus. As is well known a baseline restorer can be thought of as a switched C-R network. A switch enables the C-R differentiator along the baseline and excludes it on the signal. At moderate count rates, time constant CR should be chosen equal or larger than three times the shaping time (tau_s), otherwise the signal-to-noise ratio of the system would worsen significantly. If tau_s is of the order of 10 mus, a recovery time as long as 30 mus must be used in the baseline restorer. A so-long time constant cannot he realized with a passive network in an integrated circuit, because large-value capacitors and resistors require a too large chip area. We have addressed this issue by using a switchable current-conveyor structure that behaves like a large-value resistor. A switch permits to exclude the current-conveyor equivalent resistor when signals occur. The gate signal is provided by an amplitude discriminator, placed at the baseline-restorer output.