Composite INA Extends CMRR Frequency Range 10X
Posted: Sun Oct 26, 2014 12:44 pm
"Composite Instrumentation Amp Extends CMRR Frequency Range 10X," Moshe Gerstenhaber, Chau Tran, Electronic Design, February 4, 2002.
This article shows how cross-coupled "double-balanced" instrumentation amps extend, due to symmetry, high frequency common mode range. In this thread viewtopic.php?f=12&t=700 Wurcer and Kitchen describe in 1982 a "3 dB" noise advantage of cross-coupled inputs due to stacking. An additional advantage would seem to be even-order distortion cancellation. Of the three arguments for cross-coupled inputs the extension of HF CMRR range seems to be the strongest.
"Composite Instrumentation Amp Extends CMRR Frequency," Gerstenhaber, Tran, Electronic Design, February 4, 2002.
"Composite Instrumentation Amp Extends CMRR Frequency Range 10X," Moshe Gerstenhaber, Chau Tran, Electronic Design, February 4, 2002.
Full pdf: https://proaudiodesignforum.com/images/ ... 4_2002.pdf
The top curve in Figure 3 shows the CMRR of the cross-coupled pair, the bottom curve shows the CMRR of the single differential amp U1.
Note that in audio applications the advantage that cross-coupling provides for high frequency common mode improvement doesn't require U3 (figure 1) since the line receiver of a following device or stage will likely be differential as well.
In this thread I discuss this circuit: viewtopic.php?f=6&t=422&start=45
For audio applications the AD623 is not the ideal part.
A pair of single op amp line receivers such as the THAT1246, INA137 or the dual versions of them make more sense for audio.
Gerstenhaber and Chau Tran published a later article showing how a cross-coupled input can be used to drive a differential A/D. In that article U3 is replaced by the A/D's differential input and Vcm injected into the INA's reference pins.
"Measurement Circuit Features High Common-Mode Rejection," Moshe Gerstenhaber, Chau Tran, Electronic Design, July 22, 2002.
Full pdf: https://proaudiodesignforum.com/images/ ... 2_2002.pdf
Measurement Circuit Features High Common-Mode Rejection," Moshe Gerstenhaber, Chau Tran, Electronic Design, July 22, 2002
This article shows how cross-coupled "double-balanced" instrumentation amps extend, due to symmetry, high frequency common mode range. In this thread viewtopic.php?f=12&t=700 Wurcer and Kitchen describe in 1982 a "3 dB" noise advantage of cross-coupled inputs due to stacking. An additional advantage would seem to be even-order distortion cancellation. Of the three arguments for cross-coupled inputs the extension of HF CMRR range seems to be the strongest.
"Composite Instrumentation Amp Extends CMRR Frequency," Gerstenhaber, Tran, Electronic Design, February 4, 2002.
"Composite Instrumentation Amp Extends CMRR Frequency Range 10X," Moshe Gerstenhaber, Chau Tran, Electronic Design, February 4, 2002.
Full pdf: https://proaudiodesignforum.com/images/ ... 4_2002.pdf
The top curve in Figure 3 shows the CMRR of the cross-coupled pair, the bottom curve shows the CMRR of the single differential amp U1.
Note that in audio applications the advantage that cross-coupling provides for high frequency common mode improvement doesn't require U3 (figure 1) since the line receiver of a following device or stage will likely be differential as well.
In this thread I discuss this circuit: viewtopic.php?f=6&t=422&start=45
For audio applications the AD623 is not the ideal part.
A pair of single op amp line receivers such as the THAT1246, INA137 or the dual versions of them make more sense for audio.
Gerstenhaber and Chau Tran published a later article showing how a cross-coupled input can be used to drive a differential A/D. In that article U3 is replaced by the A/D's differential input and Vcm injected into the INA's reference pins.
"Measurement Circuit Features High Common-Mode Rejection," Moshe Gerstenhaber, Chau Tran, Electronic Design, July 22, 2002.
Full pdf: https://proaudiodesignforum.com/images/ ... 2_2002.pdf
Measurement Circuit Features High Common-Mode Rejection," Moshe Gerstenhaber, Chau Tran, Electronic Design, July 22, 2002