STJ Quick Start Guide v 2.01
April 1, 2021
Page 6
PREAMPLIFIER SCHEMATIC
The basic preamplifier circuit is shown below. The primary feedback elements are a 1 M
Ω
resistor (which
yields the transimpedance gain = 1 mV/nA) in parallel with a 1 pF capacitor. A secondary low-frequency
feedback loop maintains the software-selected bias voltage at the STJ input. Each preamplifier circuit
includes an STJ Input Relay, which connects its input to either the STJ detector or a local ‘dummy
detector’ resistor-capacitor network (10 k
Ω
in parallel with 2 nF). All 32 channels share the Pulser Relay,
which connects their inputs to the diagnostic pulser signal via per-channel 10 M
Ω
resistors.
Fig 3: STJ Analog front-end schematic
INPUTS, OUTPUTS AND CONTROLS
Name
Connector Type
Description
Analog Outputs 0-15
SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair preamplifier outputs
Analog Outputs 16-31
SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair preamplifier outputs
LVDS I/O
Harting
27 21 121 8006
1 diff-pair analog input is received as a pulser input
3 LVDS digital inputs – used for communications and STJ
bias voltage DAC control
1 LVDS digital output – used for communications
Custom Backplane
Eurocard
The backplane connector carries the STJ input signals,
power supply connections and the user pulser signal
Pulser selection
jumpers
2x3 2mm
2 jumpers
The header and jumpers comprise a DPST switch to
select either the software-controlled pulser signal from
the MPX-32D or a user pulser input connected via the
STJ I/O card. See photos below for jumper configuration
