TMPSNSRD-TCPL1 Microchip Technology, TMPSNSRD-TCPL1 Datasheet - Page 13

• Manufacturer Part Number: TMPSNSRD-TCPL1
• Description: BOARD RTD REFERENCE DESIGN
• Manufacturer: Microchip Technology

Specifications of TMPSNSRD-TCPL1

• Sensor Type: Temperature, Thermocouple
• Embedded: No
• Utilized Ic / Part: MCP3421, MCP9804
• Processor To Be Evaluated: MCP9804, MCP3421
• Interface Type: USB
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Interface: -
• Sensitivity: -
• Sensing Range: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Inverting Amplifier with Programmable Gain Circuits
Programmable Amplifi er Gain Using a
Digital Potentiometer
Many sensors require their signal to be amplifi ed before
being converted to a digital representation. This signal gain
may be done with and operational amplifi er. Since all sensors
will have some variation in their operational characteristics,
it may be desireable to calibrate the gain of the operational
amplifi er to ensure an optimal output voltage range.
The fi gure below shows two inverting amplifi er with
programmable gain circuits. The generic circuit (a) where R
R
amplifi er, and the simplifi ed circuit (b) which removes
resistors R
R
The simplifi ed circuit reduces the cost and board area but
there are trade-offs (for the same resistance and resolution),
Using the R
to be limited and therefore each digital potentiometer step
is a fi ne adjust within that range. While in the simplifi ed
circuit, the range is not limited and therefore each digital
potentiometer step causes a larger variation in the gain.
The feedback capacitor (C
Programmable Gain Using Digital Potentiometers
Note 1: A general purpose op amp, such as the MCP6001.
V
2
AW
, and Pot
IN
and R
V
IN
BW
1
1
1
R
and R
can be used to tune the gain of the inverting
ratio to control the gain.
and R
1
A
W
Pot
2
2
A
and just uses the digital potentiometers
1
W
resistors allows the range of the gain
Simplified Circuit (b)
Pot
Generic Circuit (a)
B
1
F
) is used for circuit stability.
B
–
+
Op Amp
+
–
Op Amp
(1)
C
F
R
2
(1)
C
F
V
OUT
V
OUT
1
,
Equation 1-1 shows how to calcultate the gain for the
simplifi ed circuit (Figure 1-1b). The gain is the ratio of the
digital potentiometers wiper position on the R
ladder. As the wiper moves away from the midscale value,
the gain will either become greater then one (as wiper moves
towards Terminal A), or less then one (as wiper moves
towards Terminal B).
The device’s wiper resistance (R
calculations. This is due to it being in series with the op amp
input resistance and the op amp input impedence is very
large.
Circuit Gain Equation
R
R
BW
AW
= # of Resistors – Wiper Code x R
=
# of Resistors
R
# of Resistors
AB
V
OUT
= – R
x Wiper Code
R
BW
AW
W
Signal Chain Design Guide
) is ignored for fi rst order
x V
IN
AB
AB
resistor
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