Electronics: Demod + 4Q FE

1. Info on demodulator: http://www.few.vu.nl/organisatie/dienst/technisch/electronica/projects/20062001/ Info on front-end system: http://www.nikhef.nl/pub/departments/et/virgo/ Electronics: Demod + 4Q FE Jo van den Brand, Second V+ review

2. Design Q2, Q3 2006 Prototype Q1 2007 2+2 Boards Q2 2007 Improvements 2007 Amplifier (noise) PCB length 8.35 MHz (band filter) Demodulator boards Han Voet, VU Amsterdam

3. RF input: white noise 20 Hz – 20 MHz, 80 mV RMS Test results • Conversion gains • Apply 6.260000 MHz on Ref, 6.260100 MHz on RF • Low 2.75, mid low 25, mid high 230, high 2000 • Cross talk • Apply 6.26 MHZ (8.35 MHz) to both reference inputs. Apply RF signal one channel (vertical/horizontal). • Board 4, 5: H/V I & Q out < 0.3% of V/H • I & Q phase 90 degree phase shift • Measured with a 50 Hz beat frequency output signal on the I & Q outputs • Phase deviation smaller than 1.5 degr • Equivalent input noise • 1 nV/rtHz (to be confirmed) Discussion: replace all demod boards

4. 4Q FE – Modeling Henk Groenstege TINA-TI Multisim

5. 1/f noise amplifier diode cap. resistor noise Modeling • Model agrees with data • DC 2x lower • RF 100 nV/rtHz (was 130 nV/rtHz) • Gives 2.5 pA/rtHz • Optimize both DC and RF

6. Front-end amplifiers • Non-linear design determined by • Diode • Capacitance • Leakage current • Feedback resistor (white noise) • Feedback capacitance • Desired bandwidth • Desired gain factor • 1/f noise • Amplifier • Voltage noise • Current noise • Input capacitances • Gain-bandwidth product • Under consideration • OPA 846 • OPA 657 • AD 8675 (6V) • ADA 4899-1 • AD 829 Avoid switching in front-end (stray capacitance)

7. Si PIN YAG 444-4AH 11 mm diameter 0.45 A/W Rev. bias 180 V (power!) 10 pF Si Centronic QD50-3T IR enhanced 0.22 A/W Rev. bias 15 V (GEO) InGaAs Q3000 3 mm diameter 0.90 A/W Rev. bias 10 V < 225 pF 24 ns rise time Photo diodes In discussion with various suppliers: OSIOptoelectronics Centronic Hamamatsu

8. InGaAs • Simulation • Unacceptable performance at 6 Mz • Bandwidth limited < 400 kHz • InGaAs • 3mm diameter type? • Ordered: will be tested

9. 4Q FE: outside • Dimensions of box roughly the same (48 * 100 * 170 mm) • Mounting tube (30 mm) on front • Same connectors and supply and steering voltages • Bias control & monitoring • New LF outputs • Same detector (YAG 444-4), but rotated to + orientation • Simple overload indication (LEDs) • Spares: orientation x • New: orientation +

10. 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, 1 Hz 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.

11. Status / issues • Front-end electronics • No switching in transimpedance stage • Two FE versions • Low power: ≤ 3 mW • High power: ≤ 30 mW • Switching possible after first stage • DC filter 3.3 kHz LP • Prototypes have been constructed • Detector board, with first stage pre-amp • Driver board • contains the cable drivers • differential amplifiers for the hor. and vert. outputs • bias generation, etc • Further studies ongoing • Improve performance • Decide on configuration • Decisions needed on switching DC and RF • Anticipate meeting in January 2008

12. Discuss switching, etc. Planning Replacement of demodulator boards

13. Summary • Demodulator boards • First systems delivered • Discuss production of additional boards • Front-end electronics • Simulation models in place • Amplifiers • Diodes • Test performance • Planning • Delivery prototype in March 2008 • Delivery all boards in July 2008

14. Results 1/f Affected by C Noise R2 Noise R1

15. Noise sources • Resistors R1 and R2 (10 k) • Noise = 4R kT BW = 4(10.000)(1.38 10-23 J/K)(295 K)(1 Hz) = 1.6  10-16 V2 • Low pass filters • fR1 = 1/2R1C2 = 1/2 (10.000 )(1.5  10-12 F)=10.6 MHz • fR2 = 1/2R2C1 = 1/2 (10.000 )(10  10-9 F)=1.6 kHz • Diode noise • Dark current 1nA (use 180 G on –180V) • Diode capacity 10 pF • Amplifier noise • Use pspice amplifier model • Includes 1/f noise, etc.