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LTC6373

Rev. 0

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APPLICATIONS INFORMATION

degrade the LTC6373’s inherent AC CMRR. To avoid any

possibility of common mode to differential mode signal

conversion, match the common mode filter frequencies

(on positive and negative inputs of LTC6373) to 1% or

better. Then the differential mode filter frequency can be

set for the bandwidth of the signal to be processed in the

application. Setting the differential mode filter frequency

close to the sensor’s bandwidth also minimizes any noise

pickup along the leads. If the sensor is an RTD or a resis-

tive strain gauge in close proximity to the LTC6373, then

the series resistors RS can be omitted. As an example, if

the bandwidth of the signal of interest is 100kHz whereas

the interference frequency is 10MHz and above, an appro-

priate choice for differential mode filter (FilterFreqDIFF)

and common mode filter (FilterFreqCM) frequencies could

be 200kHz/4MHz. Assuming RS is chosen to be 1kΩ,

using the formula provided earlier in this section results in

CC = 39pF and CD = 390pF.

Error Budget Analysis

Figure 7 shows the LTC6373 in a typical application to

buffer and amplify the differential output of a bridge trans-

ducer. The LTC6373 is programmed to a gain of 8V/V

in this example and amplifies a differential, full-scale

(FS) voltage of 100mV = 0.1V at transducer’s output

(or LTC6373’s input). Table 2 shows the error budget

in this application, listing various error sources in parts

per million (ppm) normalized to full-scale voltage (0.1V)

and across the temperature range of 25°C to 85°C. The

LTC6373 achieves superior performance compared to

all other monolithic programmable-gain instrumenta-

tion amplifiers (PGIA) in the market, enabling more

accurate measurements.

Figure 7. Precision Bridge Amplifier

6373 F07

–

LTC6373

V–

V+

15V

10k

10V

10k

G = 8

–15V

+OUT

–OUT

VOCM

Table 2. Error Budget Analysis

ERROR SOURCE

CALCULATION

ERROR, ppm OF INPUT FULL SCALE (FS)

LTC6373 (G = 8)

CLOSEST COMPETITOR

PGIA (G = 8)

LTC6373 (G = 8)

CLOSEST COMPETITOR

PGIA (G = 8)

Absolute Accuracy at TA = 25°C

Gain Error

Offset Voltage (RTI)

Input Offset Current

CMRR

0.015% FS

(104µV)/0.1V

[(25pA)(10kΩ)/2]/0.1V

[(5V)/(100dB)]/0.1V

0.05% FS

(1500μV)/0.1V

[(100pA)(10kΩ)/2]/0.1V

[(5V)/(95dB)]/0.1V

150

1040

500

15000

889

Total Accuracy Error

1691

16394

Temperature Drift to 85°C

Gain Drift

Offset Voltage Drift (RTI)

(1ppm/°C)(60°C)

[(1.8µV/°C)(60°C)]/0.1V

(10ppm/°C)(60°C)

[(6μV/°C)(60°C)]/0.1V

1080

600

3600

Total Drift Error

1140

4200

Resolution

Gain Nonlinearity

Typ 0.1Hz to 10Hz Input Voltage Noise

3ppm

(1.2µVP-P)/0.1V

20ppm

(1µVP-P)/0.1V

Total Resolution Error

Grand Total Error

2846

20624

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