Datasheet

MCP6N11
DS25073A-page 10 © 2011 Microchip Technology Inc.
1.5 Explanation of DC Error Specs
1.5.1 INPUT OFFSET RELATED ERRORS
The input offset error (V
E
) is extracted from input offset
measurements (see Section 1.4.1 “Input Offset Test
Circuit”), based on Equation 1-1:
EQUATION 1-4:
V
E
has several terms, which assume a linear response
to changes in V
DD
, V
SS
, V
CM
, V
OUT
and T
A
(all of which
are in their specified ranges):
EQUATION 1-5:
Equation 1-2 shows how V
E
affects V
OUT
.
1.5.2 INPUT OFFSET COMMON MODE
NON-LINEARITY
The input offset error (V
E
) changes non-linearly with
V
CM
. Figure 1-8 shows V
E
vs. V
CM
, as well as a linear
fit line (V
E_LIN
) based on V
OS
and CMRR. The op amp
is in standard conditions (ΔV
OUT
=0, V
DM
=0, etc.).
V
CM
is swept from V
IVL
to V
IVH
. The test circuit is in
Section 1.4.1 “Input Offset Test Circuit” and V
E
is
calculated using Equation 1-4.
FIGURE 1-8: Input Offset Error vs.
Common Mode Input Voltage.
Based on the measured V
E
data, we obtain the
following linear fit:
EQUATION 1-6:
The remaining error (ΔV
E
) is described by the Common
Mode Non-Linearity spec:
EQUATION 1-7:
The same common mode behavior applies to V
E
when
V
REF
is swept, instead of V
CM
, since both input stages
are designed the same:
EQUATION 1-8:
1.5.3 DIFFERENTIAL GAIN ERROR AND
NON-LINEARITY
The differential errors are extracted from differential
gain measurements (see Section 1.4.2 “Differential
Gain Test Circuit”), based on Equation 1-2. These
errors are the differential gain error (g
E
) and the input
offset error (V
E
, which changes non-linearly with V
DM
):
EQUATION 1-9:
These errors are adjusted for the expected output, then
referred back to the input, giving the differential input
error (V
ED
) as a function of V
DM
:
EQUATION 1-10:
V
E
V
M
V
REF
–
G
DM
1g
E
+()
---------------------------------=
Where:
PSRR, CMRR and A
OL
are in units of V/V
Δ T
A
is in units of °C
V
DM
=0
V
E
V
OS
Δ V
DD
Δ V
SS
–
PSRR
---------------------------------
Δ V
CM
CMRR
-----------------
Δ V
REF
CMRR
-----------------+++=
Δ V
OUT
A
OL
----------------- Δ T
A
Δ V
OS
Δ T
A
------------- ⋅ ++
V
1
V
3
V
E
, V
E_LIN
(V)
V
CM
(V)
V
IVL
V
IVH
V
DD
/2
V
2
V
E_LIN
V
E
ΔV
E
Where:
V
E_LIN
V
OS
V
CM
V
DD
2 ⁄ –
CMRR
-----------------------------------+=
V
OS
V
2
=
1
CMRR
-----------------
V
3
V
1
–
V
IVH
V
IVL
–
------------------------------=
Where:
INL
CM
max Δ V
E
V
IVH
V
IVL
–
------------------------------=
Δ V
E
V
E
V
E_LIN
–=
V
E_LIN
V
OS
V
REF
V
DD
2 ⁄ –
CMRR
-------------------------------------+=
INL
CM
max Δ V
E
V
IVH
V
IVL
–
------------------------------=
G
DM
1R
F
R
G
⁄ +=
V
M
G
DM
1g
E
+()V
DM
V+
E
()=
V
ED
V
M
G
DM
------------V
DM
–=