Differential Preamp
description
Transcript of Differential Preamp
Differential Preamp
Stephen Kaye
2013-3-22
New Preamp Design Motivation
• Move preamplifier from controller to the Vacuum Interface Board (VIB)
• Amplifies signal near the CCDs– Larger signal less
susceptible to noise during transmission
• Use dummy CCD output to create differential transmission– Decrease susceptibility to
noise and crosstalk by creating and transmitting a differential signal
Preamp Design
DifferentialInput from CCD
AC Coupled
DC Black Level Clamp
Preamp Design (Generic)
Preamp Design - Gain
• Image area full well is 275,000e- (Adjust clocks not to exceed this.)
• 16 bit ADC differential input voltage range is +- 4.096V (AD7625)
• Map this to 60,000 ADU, so conversion gain = 4.6e-/ADU
• CCD sensitivity = 7 µV/e-
• Total video gain = 1.95 V/V
• All video gain is in preamp stage
Preamp Design – Black Level Clamp
• Switch connects AC coupling capacitors to ground
• Switch activated during vertical transfers
• Transients from switch are coupled to both inputs and are common mode
Preamp Design - Noise
Preamp Design - NoiseInput Referred Voltage Noise
CCD Source Follower
40 nV/√Hz
Source Follower Load Resistor
4.7 nV/√Hz
Op-Amp Feedback Resistor
1.4 nV/√Hz
Op-Amp Bridge Resistor
4 nV/√Hz
Op-Amp Input Voltage Noise
2.8 nV/√Hz
Op-Amp Input Current Noise
1.5 nV/√Hz
Clamp Leakage Current Noise
0.125 pV/√Hz
Preamp Design – Output Impedance
• Preamp is driving twinax cables
• Twinax cable impedance is 100 Ω
• Series resistors are 100 Ω for serial termination