Output common-mode rejection (OCMR) is defined as the change in differential output voltage due to a change in output common-mode voltage. When measuring OCMR，VIN is grounded and a common-mode voltage，VCM， is applied to the output as shown in Figure 4. Ideally no differential mode signal (VOD) should appear. However， a small mode-conversion effect causes an error signal whose magnitude is quantified by OCMR.
Output common-mode rejection (OCMR) is defined as the change in differential output voltage due to a change in output common-mode voltage. When measuring OCMR，VIN is grounded and a common-mode voltage，VCM， is applied to the output as shown in Figure 4. Ideally no differential mode signal (VOD) should appear. However， a small mode-conversion effect causes an error signal whose magnitude is quantified by OCMR.
Finally，many people believe that perfect signal balance is required to reject noise in balanced interfaces. While signal balance helps maintain headroom， it does not affect the common-mode rejection of the source/receiver system (impedance balance and CMR is what counts to reject hum and noise).
Especially in discrete balanced output stages, some designers trim signal balance by using a pot connected between the two outputs with its wiper grounded. (See Figure 2 .) But，the best CMR of the source/receiver system occurs at a very different setting from that which achieves best signal balance. Of course， this concern can be largely eliminated by turning to the popular integrated solutions， which guarantee high common-mode rejection through careful trimming of the internal resistors.
发表于 2023-10-16 11:25
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