1. HPD with external readout
INFN Milano Bicocca
April 2010
HPD with external readout
Claudio Gotti

2. HPD with external readout
A monolithic charge sensitive preamplifier was designed in our labs, exploiting a 90-nm CMOS technology from TSMC.
The preamplifier was tailored for the characterization with nanosecond resolution of a diamond detector, giving signals of about 10 kel, with detector capacitance of 1 pF to 5 pF.
→ Similar to the requirements of an external readout for the upgrade of HPDs

3. HPD with external readout
The approach is the classic opamp-based charge sensitive preamplifier:
→ the feedback capacitor Cf is 50 fF
→ the feedback resistor Rf is 250 kOhm

4. HPD with external readout
The opamp has 3 gain stages and is undercompensated for ~ 500 MHz bandwidth at
→ Cd = 20 Cf = 1 pF
→ Cd = 100 Cf = 5 pF
A control pin allows to choose between the two possibilities.
The opamp input capacitance is Ca = 250 fF

5. HPD with external readout
Simulated 10 kel to 50 kel charge response with Cd = 1pF:

6. HPD with external readout
The output can drive 50 ohm terminated cable
(although with a slower risetime):
Power dissipation
Rise Time
Without load
With W load
7 mW
350 ps
700 ps
5 mW
500 ps
800 ps
4 mW
650 ps
1 ns
3 mW
1.1 ns

7. HPD with external readout
Opamp input series noise is less than 1 nV / sqrt(Hz) at high frequency:

8. HPD with external readout
The Equivalent Noise Charge (ENC) is given by:
The feedback resistor gives the parallel noise contribution.
With a 10 ns shaping time, we expect
Source (detector) Capacitance
ENC
( t = 10 ns )
( t = 5 ns )
0 pF
160 el
116 el
1 pF
180 el
2pF
215 el
230 el
5 pF
350 el
480 el

9. HPD with external readout
Chip layout: (300 um x 250 um – can be reduced)