![background image](http://html1.mh-extra.com/html/national-instruments/ni-pxi-1042-series/ni-pxi-1042-series_quick-start-manual_3444618005.webp)
STJ Quick Start Guide v 2.01
April 1, 2021
Page 4
Analog Inputs 16-31
SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair analog inputs
LVDS I/O
Harting
27 21 121 8006
1 diff-pair analog output is driven by a 14-bit high-speed
DAC, i.e. the built-in pulser signal
3 LVDS digital outputs – used for communications and
STJ bias voltage DAC control
1 LVDS digital input – used for communications
PXI Backplane
Standard
PXI / CompactPCI 33MHz 32-bit interface
BANKS AND CHANNELS
The 32-channels are divided among 4 ‘Banks’ of 8 channels, each, due to the use of octal ADCs and octal
VGAs. Channels 0-7 comprise Bank0, Channels 8-15 comprise Bank1, Channels 16-23 comprise Bank2,
Channels 24-31 comprise Bank3. Note that some DSP parameters, e.g. BANK0ADCGAIN, BANK3ADCNYQ,
operate at the Bank level, and are thus duplicated 4 times with the Bank identifier (ranging 0-3) included
in the name.
VARIABLE GAIN
The analog signal gain passes through a software controlled octal variable-gain amplifier (VGA) stage. The
VGA is controlled at the Bank level by the DSP parameters BANK0ADCGAIN, BANK1ADCGAIN,
BANK2ADCGAIN and BANK3ADCGAIN.
The digitized signal can be approximately expressed in units of ADC least-signficant-bits (LSB) as:
ADC [LSB] = 10^((BANKnADCGAIN-5)/20) * input signal [mV]
For example, with BANK0ADCGAIN = 20, a 100 mV signal on channels 0-7 yields an ADC amplitude of
approximately 576 LSBs. Note that the STJ Analog transimpedance gain is 1 mV/nA, so the gain can also
be expressed as:
ADC [LSB] = 10^((BANKnADCGAIN-5)/20) * STJ signal current [nA]
SAMPLE RATE
The on-bard octal ADC’s digitize the preamplifier signals at 50 MS/s, i.e. the sampling interval is 20 ns.
ENERGY SCALING
Digital trapezoidal filtering is used to improve the signal-to-noise in order to optimize the energy
(amplitude) measurement. The filter includes a fine-grain digital scaling factor
Needs work!!!
Note that analog variable gain and digital scale factor are controlled in ProSpect via the Preamp Gain,
Dynamic Range and MCA Bin Width settings…
STJ ANALOG MODULE