User manual

MCP6V01 Input Offset Demo Board User’s Guide
DS51801A-page 10 © 2009 Microchip Technology Inc.
2.4 OPERATING CONDITIONS
This board works most effectively at room temperature (near +25°C). Measurements
at other temperatures should be done in an oven where the air velocity is minimal.
The power supply (V
DD
) should be between 1.8V and 5.5V.
The common mode voltage (V
CM
) needs to be between 0.3V and V
DD
– 0.3V for proper
operation of this demo board.
2.5 CALCULATING THE DUT’S INPUT OFFSET VOLTAGE
The DUT’s total input offset voltage (V
OST
) can be calculated from a measurement as
shown in Equation 2-1.
EQUATION 2-1:
2.6 CONVERTING INPUT OFFSET VOLTAGE TO OTHER PARAMETERS
2.6.1 Theory
Changing the bias voltages changes the input offset voltage. Microchip’s application
note AN1177 discusses in detail how these changes in V
OS
are related to specifications
found in our data sheets. The following list summarizes the parameters that contribute
to V
OST
:
• Specified Input Offset Voltage:
-V
OS
= Input offset at the specified bias point
• DC Common Mode Rejection Ratio:
- CMRR = ΔV
CM
/ΔV
OS
• DC Power Supply Rejection Ratio:
- PSRR = (ΔV
DD
– ΔV
SS
)/ΔV
OS
• DC Open-Loop Gain:
-A
OL
= ΔV
OUT
/ΔV
OS
• Input Offset Drift over Temperature:
- ΔV
OS
/ΔT
A
V
OST
V
M
V
DD
2⁄–()1G
DA
G
N
()⁄()⋅=
Where:
1/(G
DA
G
N
) ≈ 10.0 µV/V
Note: The data sheet Input Offset Voltage (V
OS
) specification applies to one bias
point and temperature only. The total input offset voltage (V
OST
) includes
V
OS
and other changes in input offset as bias voltages and temperature
change.