Transcript Template Pecha Kucha

ProtoSmart Board: ADC Input Stage
by
Clayton Bridge
ProtoSmart Board
The Problem
ProtoSmart Board Design Specifications:
Voltage Measurement Minimum:
Voltage Measurement Maximum:
Current Measurement Minimum:
Current Measurement Maximum:
measured across a 0.2Ω current sense resistor:
- 10
+ 10
-1
+1
+/- 0.2
V
V
A
A
V
-2
+2
V
V
ADC Specifications:
ADC Range (IN+ - IN-) Minimum:
ADC Range (IN+ - IN-) Maximum:
The Real Problem
The Caveat:
IN+ and IN- range:
0 - 3.3V
Summary:
ADC wants to see -2 to 2V range DIFFERENCE between IN+ and INBUT
IN+ and IN- MUST remain between 0 – 3.3V
The Solution (Vaguely)
The Solution (Mathematically)
Minimum Signal Representation:
Voltage:
Current:
IN+
INADC_out
-10V
-1A (-0.2V across Rsense)
0V
2V
-2V
Maximum Signal Representation:
Voltage:
Current:
IN+
INADC_out
+10V
+1A (+0.2V across Rsense)
2V
0V
+2V
The Solution (Conceptually)
What are we doing again?
Massage the measurement signal to covert it to a 0-2V range and feed to IN+.
Feed (2 – IN+) to INConverting ProtoSmart Board measurement range to -2 to 2V for ADC.
The Solution (Functionally)
The Solution (Electronically)
Divide and Conquer
How?
Examine each function or stage separately and observe their effect on the signal.
We will input a 20Vpp sine wave centered at 0V representing the +/-10V measurement
signal and observe the output after each stage.
Vin: Unity Gain Instrumentation Amplifier
Scaling Stage: Inverting Amplifier
V_DIF
vout_scaled
Shifting Stage: Noninverting Summing Amplifier
V(vadc+)
VADC- : Unity Gain Instrumentation Amplifier
vadc-
2V
Overall Effect
Choosing the Op Amps
ProtoSmart Board Specifications
Frequency range:
Voltage range:
Factors to Consider
Gain-bandwidth Product
Slew Rate
Output Voltage Swing
Price
< 1MHz
+/- 10V
Specifications to Prevent Distortion
GBW > 1MHz
SR > 7 V/us
Rails > 0 to +2V
GBW > 1MHz
SR > 7 V/us
Rails > 0 to +2V
GBW > 1MHz
GBW > 5MHz
SR > 63 V/us
Rails > -10 to +10V SR > 7 V/us
Rails > -10 to +10V
Rails > 1V
I hope you enjoyed this little Pecha
Kucha!