SBAA532A February 2022 – March 2024 ADS1119 , ADS1120 , ADS1120-Q1 , ADS112C04 , ADS112U04 , ADS1130 , ADS1131 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1158 , ADS1219 , ADS1220 , ADS122C04 , ADS122U04 , ADS1230 , ADS1231 , ADS1232 , ADS1234 , ADS1235 , ADS1235-Q1 , ADS124S06 , ADS124S08 , ADS1250 , ADS1251 , ADS1252 , ADS1253 , ADS1254 , ADS1255 , ADS1256 , ADS1257 , ADS1258 , ADS1258-EP , ADS1259 , ADS1259-Q1 , ADS125H01 , ADS125H02 , ADS1260 , ADS1260-Q1 , ADS1261 , ADS1261-Q1 , ADS1262 , ADS1263 , ADS127L01 , ADS130E08 , ADS131A02 , ADS131A04 , ADS131E04 , ADS131E06 , ADS131E08 , ADS131E08S , ADS131M02 , ADS131M03 , ADS131M04 , ADS131M06 , ADS131M08
Figure 2-6 illustrates how it is possible to eliminate the non-linearity in a bridge with two active elements in opposite branches by using current excitation instead of voltage excitation.
Equation 8 calculates the resulting output voltage, VOUT, when IEXCITATION splits between each branch of the bridge in Figure 2-6.
The ratio (2 ∙ R + ΔR) / (4 ∙ R + 2 ∙ ΔR) in Equation 8 reduces to ½, which produces the simplified result in Equation 9:
Unlike the circuit using voltage excitation, Equation 9 has no ΔR term in the denominator. As a result, current excitation removes the non-linearity error due to the topology of a bridge with two active elements in opposite branches. Comparatively, the same circuit using voltage excitation has a non-linearity error proportional to 2 ∙ R + ΔR.
A bridge measurement system using current excitation has additional benefits and challenges. Refer to Section 6.5 for more information about how this circuit is implemented.