1712 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 43, NO. 3, JUNE 1996 Baseline Restoration Using Current Conveyors zyx Antonio Miguel L. S. Morgado, J. Basilio SimGes, Carlos M. Correia Physics Department - University of Coimbra P-3000 Coimbra - PORTUGAL zyxwv Abstract This paper presents simple circuits for baseline restoration based on a commercial current conveyor (CCIIOl). Tests were performed, on two circuits, with periodic trapezoidal shaped pulses in order to measure the baseline restoration for several pulse rates and restorer duty cycles. For the current conveyor based Robinson restorer, the peak shift was less than 10 mV, for duty cycles up to 6O%, at high pulse rates. Duty cycles up to 80 zyxwvutsrq YO were also tested, being the maximum peak shift 21mV. The peak shift for the current conveyor based Grubic restorer was also measured. The maximum value found was 30 mV at 82% duty cycle. Keeping the duty cycle below 60% improves greatly the restorer performance. The ability of both baseline restorer architectures to reject low frequency modulation is also measured, with good results on both circuits. zyxwvutsr I. INTRODUCTION zyxwvu A good perfomance of high resolution nuclear spectrometry systems, at high pulse rates, demands restoration of baseline between pulses, in order to remove rate dependent baseline shifts. This restoration is performed by circuits named baseline restorers (BLRs) which also remove low frequency noise, such as power supply hum and detector microphonics. Current conveyors, with the features inherent to their architecture (current output and the absence of negative feedback), have attracted considerable attention since they were introduced in 1968 [l]. The concept was enhanced in 1970 with the so called second generation current conveyors (CCII) [2]. These are three port networks. The relationship between the network terminals is given by: O O O V , zyxwvut [t] = [l 0 +1 0 o ! ; . ] 0 v, Until recently, there were not any current conveyors commercially available as a monolhitic integrated circuit. Since last year, a dual positive second generation current conveyor is available, in a 8 pin dual in line package. This device [3], named CCIIO1, features 2000 V/ps slew rate and 700 MHz equivalent gain-bandwidth, with a good CMRR performance (better than 53 dBs at 1 MHz). These characteristics, along with absence of feedback, make high speed circuit design a lot easier and suggests the reformulating of classical circuits. 0018-9499/96$05 This work reports the use of the CCIIOl current conveyor in baseline restorers . We present two versions of the classical Robinson restorer, and their testing results. Current Conveyors configurations for feedforward zyx type baseline restorers are also presented. 11. CIRCUITS The CCII01 current conveyor lends itself to differential input configurations that readily configures a preliminary version of the Robinson BLR [4], as the one depicted in Fig.1 (a), In this circuit, restoration of the baseline occurs whenever the level of the output is negative. The value of the restoring current is determined by the resistor R while the diode makes this action unidirectional. IN - Fig 1. Single (a) and double (b) conveyor configurations of the Robinson BLR. The double conveyor configuration, Fig. 1 (b), essentially follows the same working principles allowing for the fine setting of the restoration level through the trimmer at the high impedance zyxwv Y input of the upper conveyor. In order to restore pulses with spurious tails (as is the case in imperfect adjustment of Pole-Zero cancellation), the trimmer must be .OO 0 1996 IEEE