5 10x Gain Amplifier
The 10x Gain amplifier (figure 8) uses a differential amplifier together with capacitive gain to amplify
the signals from the preamplifier and shaper prior to applying these to the comparators. This is
necessary since the required minimum signal required at the output of the shaper would be of the
order of 2mV, which is insufficient to set a comparator threshold. There is a feedback circuit which
provides DC stability and a circuit which is used to reset the amplifier. The circuit is configurable for
holes or electrons. In both modes the amplifier is biased at 1.5V.
RST
110fF
From
1.1pF
Resistive Feedback
Preamp/
Shaper
To
Comparator
VPRE10 / VSHA10
Figure 8: 10x Gain Amplifier.
5.1 Offset Cancellation
The 10x Gain Amplifiers form the input to the comparators. The amplifiers and comparators will
have some offset associated with them which will vary from channel to channel. In order to cancel
this out, the differential amplifiers have a programmable offset which is used to trim the input to the
comparators. This can be trimmed in a positive or negative direction over a few hundred mV to 7
bits resolution.
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