6 Comparators
There are two identical comparators used within each channel. The first one is connected to the 10x
Gain Amp connected to the preamplifier and a programmable threshold voltage is used to generate
a timestamp from the fast leading edge of the preamplifier output. The second comparator is
connected to the 10x gain amplifier connected to the shaper and a second programmable threshold
voltage is used to define the signal energy level at which a "hit is generated. Only signals above this
level are read out. Although there is no circuit to specifically reset the comparator, the outputs from
the comparators are latched within the channel control logic and these latches require resetting. A
polarity switch determines whether it is working in holes or electrons mode.
7 Peak Hold Circuit
The peak hold circuit connects to the output of the shaper where it follows the signal on its output
before holding the peak of the voltage. The circuit contains two amplifiers, one is used when reading
holes the other used when reading electrons. The amplifier not used in the peak hold configuration
is used as a sample and hold buffer. An additional circuit provides a small trickle current which
biases the peak hold circuit up as a slow buffer. When the energy threshold comparator fires, this
trickle current is switched off and the circuit switches to peak hold configuration. The small trickle
current means that the peak hold circuit does not require periodic resetting, but only requires
resetting once the channel has been read out.
Sample
From
V S H A
Shaper
SampleB
1 s t a g e
d i f f
a m p
SampleB
V P H
C P H
T r i c k l e
C u r r e n t
Sample
1 s t a g e
d i f f
To Analogue
C S H
a m p
Multiplexer
V O U T
Figure 9: Peak Hold in Holes Configuration
10