Datasheet

LMC6041

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SNOS610E –DECEMBER 1994–REVISED MARCH 2013

(Input pins are lifted out of PC board and soldered directly to components. All other pins connected to PC board.)

Figure 35. Air Wiring

Typical Single-Supply Applications

= 5.0 V

)

The extremely high input impedance, and low power consumption, of the LMC6041 make it ideal for applications

that require battery-powered instrumentation amplifiers. Examples of these type of applications are hand-held pH

probes, analytic medical instruments, magnetic field detectors, gas detectors, and silicon based pressure

transducers.

Figure 36. Two Op-Amp Instrumentation Amplifier

The circuit in Figure 36 is recommended for applications where the common-mode input range is relatively low

and the differential gain will be in the range of 10 to 1000. This two op-amp instrumentation amplifier features an

independent adjustment of the gain and common-mode rejection trim, and a total quiescent supply current of less

than 28 μA. To maintain ultra-high input impedance, it is advisable to use ground rings and consider PC board

layout an important part of the overall system design (see Printed-Circuit-Board Layout for High Impedance

Work). Referring to Figure 36, the input voltages are represented as a common-mode input V

plus a

differential input V

Rejection of the common-mode component of the input is accomplished by making the ratio of R1/R2 equal to

R3/R4. So that where,

(3)

A suggested design guideline is to minimize the difference of value between R1 through R4. This will often result

in improved resistor tempco, amplifier gain, and CMRR over temperature. If RN = R1 = R2 = R3 = R4 then the

gain equation can be simplified:

(4)

Due to the “zero-in, zero-out” performance of the LMC6041, and output swing rail-rail, the dynamic range is only

limited to the input common-mode range of 0V to V

–2.3V, worst case at room temperature. This feature of the

LMC6041 makes it an ideal choice for low-power instrumentation systems.

Product Folder Links: LMC6041