4 Shaper
RST
500f
500f
1p
2p
4p
RST
1.3pF
1M
1.3pF
2.6pF
To
Peak Hold
5.2pF
240k
10.4pF
From
Preamp
VSHA
Figure 5: Programmable CR-RC Shaper
The shaper (figure 5) is comprised of a differential amplifier, a resistor and capacitor network in
series with the input, and a resistor and capacitor network in feedback across the amplifier, all
forming a CR-RC shaping configuration. The amplifier is biased up with a programmable voltage and
the shaping time is selectable between 0.5us and 8us using the programmable capacitor arrays. As
with the preamplifier, the shaper is configurable for reading both electrons and holes (by changing
the bias voltage VSHA) and there is a circuit for resetting the shaper.
4.1 Shaper Response
Figure 6 shows the shaper response to a signal while in electrons mode. The signal is negative going
so the shaper needs to be biased at about 2.4V. For Holes the signal would be positive going so the
shaper should be biased at 0.6V.
7