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Electronics: Demod + 4Q FE

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Demodulator boards

• Design Q2, Q3 2006• Prototype Q1 2007• 2+2 Boards Q2 2007

• Amplifier (noise)• PCB length• 8.35 MHz (band filter)

Han Voet, VU Amsterdam

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4Q FE: outside

• Dimensions of box roughly the same (50 * 100 * 150 mm).• Mounting tube (30 mm) on front.• Same connectors and supply and steering voltages. • One more Lemo for bias monitoring.• New LF outputs.• Same detector (YAG 444-4), but rotated to + orientation.• Simple overload indication (LEDs).

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4Q FE: inside

• Total redesign (old → new):• First stage 2 kV/A → 10 kV/A• DC output amp. 5*, roll off at 100 Hz to 1*, passive pole at

35 Hz (if load > 50 kΩ) → cable driver 1*, pole at 100 kHz. • Extra LF outputs, 1Hz to 100 kHz.• HF outputs amp. 20*, second order high pass 30 kHz,

assumed BW 25 MHz → amp. 4*, 800 kHz … 25 MHz.• Bias monitor

– Output with a scale -1/40, -200 V bias gives +5V.– Can be connected to the ADC instead of the existing direct feedback

from the steering DAC.

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Status• Components needed for CAD design defined.• Detector board, with first stage pre-amp, layout made.• Driver board in progress. This board contains the cable

drivers, differential amplifiers for the hor. and vert. outputs, bias generation etc. Takes about two more weeks. Production, assembly and test, another ~8 weeks.

• “Exotic” components ordered.• Housing under investigation.

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Implementation Plan (updated March 2007)

2006 2007 2008

Tasks and Deliverables 1-3 4-6 7-910-

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1-3 4-6 7-910-

12

1-3 4-6 7-910-

12

Tasks

Documentation of 4440 modules

Design demodulator

Test prototype demodulator

Design FE

Test FE prototype

Test QD prototypes

Deliverables

3 Spare demodulators

2 Prototypes QD+FE

14 New QD+FE

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Questions• Remarks on the proposed roll off frequencies?• Can the proposed LF output replace the whitening filter?

(the amplifications and cut offs can be easily adjusted) More ADC channels are needed in this case. But hard to control variations between channels (especially phase errors) are avoided and compensations (loop stability) are much easier.

• Should the mounting position be moved from the front ‘pipe’ to the side of the box?

• Which output (HF or DC) is most noise critical?

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NoiseThe input referenced noise of the first stage is:

The input current noise dominates at low frequencies. The input voltage noise, together with the capacitance of the detector diode, shows up at higher frequencies. The current design has a single op-amp per channel with reasonable noise figures. This can be further improved when needed.

2 22 ( 2 )4

3N N D

A NF F

E E F CkT AI IHzR R

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BiasThe bias voltage will be fully on (-180 V) when -5 V is applied. It is off at 0 V or above. Between 0 and -5 V it reacts proportional. There is a monitor output with a scale -1/40, -200 V bias gives +5V. This can be connected to the ADC instead of the existing direct feedback from the steering DAC.It is not 100% clear whether this exactly how the previous version reacts, but seems to be compatible.