Electronics: Demod + 4Q FEJo van den Brand, Second V+ review

Demodulator boardsDesign Q2, Q3 2006Prototype Q1 20072+2 Boards Q2 2007

Improvements 2007Amplifier (noise)PCB length8.35 MHz (band filter)Han Voet, VU Amsterdam

Test resultsConversion gainsApply 6.260000 MHz on Ref, 6.260100 MHz on RFLow 2.75, mid low 25, mid high 230, high 2000Cross talkApply 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/HI & Q phase 90 degree phase shiftMeasured with a 50 Hz beat frequency output signal on the I & Q outputsPhase deviation smaller than 1.5 degrEquivalent input noise1 nV/rtHz (to be confirmed)Discussion: replace all demod boards

4Q FE ModelingTINA-TIMultisimHenk Groenstege

ModelingModel agrees with dataDC 2x lowerRF 100 nV/rtHz (was 130 nV/rtHz)Gives 2.5 pA/rtHzOptimize both DC and RF

Chart1

11802500

3501100

200500

110420

120210

70100

4758

3523

3414

3014

New DC

old

f [ Hz ]

V_DC [ nV/rt(Hz) ]

DC noise

Sheet1

HzNew DCold

1.211802500

2.53501100

5200500

10110420

20120210

5070100

1004758

2003523

5003414

10003014

Sheet1

New DC

old

f [ Hz ]

V_DC [ nV/rt(Hz) ]

DC noise

Sheet2

Sheet3

Front-end amplifiersNon-linear design determined byDiodeCapacitanceLeakage current Feedback resistor (white noise)Feedback capacitance Desired bandwidth Desired gain factor 1/f noise AmplifierVoltage noiseCurrent noiseInput capacitancesGain-bandwidth product Under considerationOPA 846OPA 657AD 8675 (6V)ADA 4899-1AD 829Avoid switching in front-end(stray capacitance)

Photo diodesSi PIN YAG 444-4AH11 mm diameter0.45 A/WRev. bias 180 V (power!)10 pFSi Centronic QD50-3TIR enhanced0.22 A/WRev. bias 15 V (GEO)InGaAs Q30003 mm diameter0.90 A/WRev. bias 10 V< 225 pF24 ns rise timeIn discussion with various suppliers: OSIOptoelectronics Centronic Hamamatsu

InGaAsSimulationUnacceptable performance at 6 MzBandwidth limited < 400 kHzInGaAs3mm diameter type?Ordered: will be tested

4Q FE: outsideDimensions of box roughly the same (48 * 100 * 170 mm)Mounting tube (30 mm) on frontSame connectors and supply and steering voltagesBias control & monitoringNew LF outputsSame detector (YAG 444-4), but rotated to + orientationSimple overload indication (LEDs)Spares: orientation xNew: orientation +

4Q FE: insideTotal redesign (old new):First stage 2 kV/A 10 kV/ADC output amp. 5*, roll off at 100 Hz to 1*, passive pole at 35 Hz (if load > 50 k) 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 monitorOutput with a scale -1/40, -200 V bias gives +5V.

Status / issuesFront-end electronicsNo switching in transimpedance stageTwo FE versionsLow power: 3 mWHigh power: 30 mWSwitching possible after first stageDC filter 3.3 kHz LPPrototypes have been constructedDetector board, with first stage pre-ampDriver boardcontains the cable driversdifferential amplifiers for the hor. and vert. outputsbias generation, etcFurther studies ongoingImprove performanceDecide on configurationDecisions needed on switching DC and RFAnticipate meeting in January 2008

PlanningReplacement of demodulator boards

SummaryDemodulator boardsFirst systems deliveredDiscuss production of additional boardsFront-end electronicsSimulation models in placeAmplifiers DiodesTest performancePlanningDelivery prototype in March 2008Delivery all boards in July 2008

Results1/fNoise R2Noise R1Affected by C

Noise sourcesResistors 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 V2Low pass filtersfR1 = 1/2R1C2 = 1/2 (10.000 )(1.5 10-12 F)=10.6 MHzfR2 = 1/2R2C1 = 1/2 (10.000 )(10 10-9 F)=1.6 kHzDiode noiseDark current 1nA (use 180 G on 180V)Diode capacity 10 pFAmplifier noiseUse pspice amplifier modelIncludes 1/f noise, etc.