two-stage amplifier status

test buffer – to be replaced with IRSX

isignal

• recent / final (hopefully) design uses load resistor and voltage gain stage for input; this is faster, lower noise, and more robustly stable• 3.5 V supply voltage to minimize power and to limit output to safe input range of IRSX ASIC

10×

−9×

0.5×

typical PMT pulse @ 3200 Vsingle photoelectron200 ps risetime8 mV peak (on 25 Ω load)

typical output pulse(same conditions, different event)PMT pulse @ 3200 V600 ps risetime300 mV peak (to IRSX)

G. Visser, Indiana Univ.

two-stage amplifier statusG. Visser, Indiana Univ.

arbi

trar

y sc

ale

– no

t cou

nts!

two-stage amp

(Zgain = 3188 Ω)

direct to scope

(Zgain = 25 Ω)

3200 VPMT gain ~ 3 × 105

at 3200V, 89% of pulses are >50 mV

3200V

3700V8 μV/div @ 1 MHz BW150 MHz/div

reasonably flat response-3dB BW ~750 MHzinput-referred noise ~1.33 nV/sqrt(Hz)

new front board status • connects to boardstack via pogo pins (on boardstack, landing pads on front board) enables mating with misalignment tolerance• “radical” design of signal routing using thick multilayer board with blind holes decouples PMT and readout board pad locations (both sides have their firm constraints), and reduces routing length for improved high speed signal integrity

signal trace routing in progress (90% complete)

press-fit pin receptacle for PMT (shown on preamp test board)

below here is backup / for reference / for our detailed discussion as needed

iTOP two-stage preamp updateG. Visser / IU November 11th 2013 this is the “final” circuit configuration

except:• calibration signal path still t.b.d.• resistor values may change (dependent on pcb layout parasitics)

• DC coupled• signal current return through VREF plane, AC coupled to bottom of 2nd MCP• bury the signal lines in front and carrier board for shielding (from, e.g., digital crosstalk)

• 1st stage noninverting for lowest noise and more constant input impedance• gain = 10×

• 2nd stage inverting for required output polarity• inverting amp can also be used to sum in calibration signal (without degrading risetime of PMT signal)• gain = −9× (or less...)• 3.5V supply limits output swing to protect the ASIC

• test buffer – to be replaced with IRSX

isignal

578 ps risetime300 mV peak

amplified single-photoelectron pulses @ -3200 V

a typical pulse

risetime histogram (from scope)

arbi

trar

y sc

ale

– no

t cou

nts!

Tek DPO7254C

100 mV/div1.25 ns/div

roughly 3×105 gain (see later slide)

raw single-photoelectron pulse @ -3200 V

This is a somewhat larger than average pulse:

≈200 ps risetime≈500 ps width

Voltage on 25 Ω load (double-terminated cable)

The noise and bandwidth limitations of this scope are significant here. The true pulse is likely rather faster and quieter.

2 mV/div1.25 ns/div

pulse integral spectrum @ 3200V

two-stage amp

(Zgain = 3188 Ω)

direct to scope

(Zgain = 25 Ω)

• Gate = 11 ns• Some double pulses and afterpulses are counted here• Zgain above (used for X axis scale) are design values, not calibrated

roughly 3×105 gain(average charge)

pulse peak amplitude spectrum

3200V

3700V

coun

ts (l

inea

r sca

le)

at 3200V, 89% of pulses are >50 mV

pulse peak amplitude spectrum

coun

ts (l

inea

r sca

le)

JT0298 PMT

slew rate limitation

At the observed 600 ps small-signal risetime, this becomes an issue when pulse height >≈ 800 mV.There may be an extra “time walk” due to this for large pulses; needs consideration and/or avoidance.

3200V 3700V

noise (and gain flatness)

8 μV/div @ 1 MHz BW150 MHz/div

Note this is a linear scale (to better show gain/noise flatness).The peak at ~100 MHz is a local radio station.With −90× gain, the input referred noise is about 1.33 nV/sqrt(Hz).

front board (dummy version)

front board (dummy version)

everything seems to fit fine...