How does one derive the equation
Zo = Rx * 10^(CMRR/20)
found on page 22 of the Burr-Brown application note called "IMPLEMENTATION AND APPLICATIONS OF CURRENT SOURCES AND CURRENT RECEIVERS" (sboa046.pdf)? This equation describes the circuit in Figure 51 of the application note.
http://www.ti.com/lit/an/sboa046/sboa046.pdf
thank you.