Differential Preamp Stephen Kaye

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 Differential Input 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 V (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 - Noise Input 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 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