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CMS Tracker FED Front End Module
Analogue Circuit Considerations
Draft 1.0
Rob Halsall et al.
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Signal Ranges
Opto RX Output
ADC Input
1.56 V
1.4 V
1.5 V
Common Mode
0.5 V
0.4 V
Opto RX Offset, 0.2V -> 0.56V
0.2 V
0V
0V
Limits of Opto Rx Output, assuming default opto settings - see below
1V range of header/signal + common mode -> 10 bit, 1 mV/bit
0.25V range of signal -> 8 bit, 1mV/bit
Assume Opto Rx Offset voltage closely matched across all 12 channels
Default Opto Rx Controls = 000110
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Single Stage AD8138 or equivalent
High AC current fed back to Opto Rx Output
DC Currents effecting operating point
Opto Rx ouput is a current source not voltage source
External resistor diff gain of 2
Gain is adjustable
2V peak to peak mode
1500R
VD=+3.3V
+3.3/5V
Opto Rx
750R
+ -
22R
+
100R
750R
- +
10
ADC
8138
22R
-
-3.3/5V
VD
1500R
VD/3
DAC
High AC currents fed back through feedback resistors
Causes Ripple Problem - couples directly to output
Point needs less than half LSB ripple ~500µV
Common to up to 12 channels in module
Possible cross talk between channels
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Single Stage AD8131 or equivalent
High AC current fed back to Opto Rx Output
DC Currents effecting operating point
Opto Rx ouput is a current source not voltage source
External resistor-less diff gain of 2
2V peak to peak mode
VD=+3.3V
+3.3/5V
Opto Rx
+ -
22R
+
100R
- +
10
ADC
8131
22R
-
-3.3/5V
VD
VD/3
DAC
Ripple Problem - couples directly to output
Point needs less than half LSB ripple ~500µV
High AC currents fed back through feedback resistors
Common to up to 12 channels in module
Possible cross talk between channels
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Two Stage AD8138-8131 or equivalents
Vout+ = Vin+
Vout- = 2 VOCM - Vin+
Resistor-less gain of -1
Vout+ = VOCM + Vin+
Vout- = VOCM - Vin+
External resistor-less gain of 2
2V peak to peak mode
VD=+3.3V
+3.3/5V
Opto Rx
+3.3/5V
- +
+ -
8138
8131
+ -
- +
100R
-3.3/5V
22R
+
10
ADC
22R
-
-3.3/5V
VD
VD/3
DAC
Driving High Impedance Inputs
Common to 12 channels in module
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Two stage transfer functions example
AD8131
AD8138
1.4
2
1.2
1.5
1
0.8
1
0.6
adcfs-
adcfs-
adcfs+
adcfs+
vocm
0.4
in
vocm
0.5
in
out-
0.2
outout+
0
0
1
2
3
4
1
5
2
3
4
5
-0.2
-0.5
-0.4
-0.6
-1
Opto Rx Output Offset of 0.2V
Signal swing of 1V
Rutherford Appleton Laboratory
ADC in 2 VPP Mode
ADC Common Mode VDD/3 = 1V
Instrumentation Department
27 March 2002
Single Stage EL2140 or equivalent
External resistor- less gain of 2
2V peak to peak mode
VD=+3.3V
+3.3V
+ +
Opto Rx
22R
+
10
ADC
2140
100R
- -
22R
-
-3.3V
VD
VD/3
DAC
True Differential Instrumentation Amplifier
3 op-amp internal architecture - to be confirmed
All Inputs High Impedance
Driving High Impedance Inputs
Common to 12 channels in module
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Summary
Approach
Amp type
Amp Gain Adj
Ripple
Power Estimate*
Cost
Vendor
Second Source
Package
Sim Model
AD8131/8
1 stage
Diff
Yes/No
>= LSB
85W
Low/Mod
Major
TI
µSOIC
Yes
AD8131 & 8
2 Stage
Diff
No
<<LSB
95W
High
Major
TI
µSOIC
Yes
EL2140C
1 Stage
Diff Instr
No
<<LSB
75W
Low
Intersil
No?
SOIC
Yes
EL2140C - needs further study?
* Estimated FED Power - still under study
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
9U Board Layout
Front End Envelope
130 mm
45 mm
366.7 mm
1
270 mm
8
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002
Front End Module Layout
EL2140/XC2V40/XC2V2000
33 x 40 mm
45 mm
27 x 27 mm
FPGA
XC2V1000XC2V3000
FG676
12 x 12mm
FPGA
XC2V40
CS144
Opto Rx
NGK
9 x 9 mm
ADC
AD9218
ST48
5 x 3 mm
DIFF OP-AMP
AD9218
RM8 - µSOIC
130 mm
N.B. No Passives Shown
DIFF OP-AMP
EL2140
SOIC
5 x 6 mm
FPGA
XC2V250
FG256
17 x 17mm
Double Sided
Single Sided
Rutherford Appleton Laboratory
Instrumentation Department
27 March 2002