A low noise amplifier-shaper with tail correction for the STAR detector

Abstract

A 16 channel low noise amplifier shaper has been designed for the STAR particle detector of the RHIC accelerator. The STAR Amplifier-Shaper (SAS) includes a pole/zero network which cancels the long tail of the Time Projection Chamber (TPC) signal. The tail correction can be adjusted depending on the type of gas used in the TPC. The SAS equivalent noise charge is 900 e/sub RMS//sup -/,, with 25 pf detector capacitance (the test board having 7.7 pF of parasitic capacitance), and with 80 ns shaping time (step response). The measured noise slope is 13.7 e/sub RMS//sup -//pF. The shaper pulse FWHM is adjusted at 180 ns (detector response) with /spl plusmn/4% variation over the entire dynamic range. The shaping time and the tail correction are adjusted with external voltages using MOS resistors. The gain is 16 mV/fC with a linearity of 4%. The crosstalk is about 0.36% which have a negligible effect on the position resolution. The circuit also includes an on-chip calibration system in which the test input charge is controlled by a DC voltage. The output buffer drives a 2 V swing on 50 pF output load for a total power consumption of less than 750 mW (/spl plusmn/5 Volt supply). On-chip protection diodes have also been integrated. The full custom chip has been integrated in the CMOS ORBIT 1.2 /spl mu/m technology with double polysilicon capacitors.