1.1 DC Output Voltage Specs / Model
1.1.1 IDEAL MODEL
The ideal PGA output voltage (VOUT) is:
EQUATION
VO_ideal = GVIN
VREF = VSS = 0V
where: G is the nominal gain
(see Figure 1-7). This equation holds when there are
no gain or offset errors and when the VREF pin is tied to
a low impedance source (<< 0.1Ω) at ground potential
(VSS = 0V).
1.1.2 LINEAR MODEL
The PGA’s linear region of operation, including offset
and gain errors, is modeled by the line VO_linear, shown
in Figure 1-7.
EQUATION
VO_linear = G(1 + gE)(VIN – 0.3V + VOS ) + 0.3V
VREF = VSS = 0V
The endpoints of this line are at VO_ideal = 0.3V and
VDD-0.3V. The gain and offset specifications referred to
in the electrical specifications are related to Figure 1-7,
as follows:
EQUATION
gE
=
100% ----------V----2----–----V----1-----------
G(VDD – 0.6V)
VOS
=
----------V----1----------
G(1 + gE)
G = +1
∆G ⁄ ∆TA
=
-∆---g----E-
∆TA
MCP6S21/2/6/8
VOUT (V)
VDD
VDD-0.3
V2
0.3
V1
0
0.3
0G
VIN (V)
VDD - 0.3 VDD
G
G
FIGURE 1-7:
Output Voltage Model with
the standard condition VREF = VSS = 0V.
1.1.3 OUTPUT NON-LINEARITY
Figure 1-8 shows the Integral Non-Linearity (INL) of the
output voltage.
EQUATION
INL = VOUT – VO_linear
The output non-linearity specification in the electrical
specifications is related to Figure 1-8 by:
EQUATION
VONL
=
-m----a---x---{----V----4--,---V----3---}-
VDD – 0.6V
INL (V)
V4
0
V3
0.3
0G
VIN (V)
VDD - 0.3 VDD
G
G
FIGURE 1-8:
Output Voltage INL with the
standard condition VREF = VSS = 0V.
2003 Microchip Technology Inc.
DS21117A-page 7