Transcript Retine artificielle

~ GADC ~
Multipurpose 10bit ADC
Denis Fougeron, Fabrice Gensolen, Mohsine Menouni, Laurent Perrot
CPPM - CNRS - Université de la méditerranée - Marseille
ATLAS pixel chip upgrade meeting – FEI4_A design
March 3rd, 2010
1
Outline
 Purpose and specifications
 General architecture
 I/Os interface
 Final layout
 Simulation results
 Summary of performances
2
Purpose and specifications

The bloc GADC (General Analog to Digital Converter) is a general purpose 10 bits ADC
used to digitize different analog voltages of the FEI4 chip.

The input voltages of the GADC will be:
- the TEMPSENS bloc output voltage to monitor the temperature of the chip,
- an image of the power supplies,
- the detector leakage current driven by the FEND bloc.

Initial specifications were :
Specification
3
Value
Resolution
10 bits
Conversion time
~ 1 us
Input voltage range to convert
0 to Vref (with Vref ≥ 900 mV)
General architecture
Input voltages
Analog 8to1 mux
GADCsel<2:0>
Selected voltage
GADCcompIbias
GADCvref
Comparator
DAC
SAR Control Logic
GADCstart
GADCout <9:0>
4
GADCclk
GADCstatus
GADCdisable
Analog I/Os interface
Pin Name
Output TO
INOUT?
Description
Specs if any
FEND
Mirrors 5X the
detector DC
leakage current.
Vtemp
TEMPSENS
Voltage for
temperature
measurement
GADCvref
Voltage
reference
Input voltage
reference for the
DAC
900 mV
GADCcompIbias
FEI4_A_
DACS
Bias current for the
comparator
10 uA
IleakIn
5
Input From
Comments and
requests
I/V conversion of this
detector leakage current
via a 100kΩ resistor
Digital I/Os interface
Pin Name
GADCsel
GADCstart
Input From
6
Description
Specs
if any
Comments and requests
Input voltage selection via
the analog Mux
3 bits selection for the 8
to 1 analog multiplexor
Control
When “high”: ask for a
conversion
The conversion starts
only when GADCstart is
“high”
Control
Control
Control
“high” when the conversion
is on-going, “low” when it is
done.
40 MHz clock for control
logic
CLKGEN
GADCout
GADCdisable
INOUT?
Control
GADCstatus
GADCclk
Output
TO
10 bits GADC output value
Active “high”. GADC bloc is
“ON” when GADCdisable is
“low” and “OFF” when
“high”.
Internal GADC clock is
1.25 MHz (it is generated
dividing the 40 MHz
input clock by 32)
Final layout
SAR
DAC
COMP

AREA = 434 x 228 um2
7
Typical and worse case simulation results
Linearity error in LSB*
vs. Input voltage
Error (LSB)
4
TT 27°C
SS 40°C
3
2
1
0
0
200
400
600
800
VthIn (mV)
*
8
linearity error = GADC_output_code - Ideal_output_code
1000
1200
1400
Quantization error of the DAC
DAC10b's quantization error
Error (V)
5,00E-04
4,00E-04
¼ LSB = 0.366 mV
3,00E-04
2,00E-04
1,00E-04
0,00E+00
0
128
256
384
512
640
768
896
1024
-1,00E-04
-2,00E-04
-3,00E-04
Corner TT T=25°C
Corner SS T=40°C
Corner FF T=-40°C
-4,00E-04
9
Summary of performances
Parameter
10
Value
Resolution
10 bit
Conversion time
10.4 us (Fclock= 1.25 MHz = 40/32)
Input voltage range to convert
0 to 1.5 V (Vref = 1.5V here)
Linearity error
1 LSB
Power consumption (when ON)
120 uA @ 1.5 V
DAC output voltage mismatch
< 800 uV p-p
Area
434 x 228 = 100 000 um²