212X8-DSH-001-B Datasheet, PDF (8/18 Pages) M/A-COM Technology Solutions, Inc. – SD and HD/SD-SDI Digital Video Cable Drivers

Functional Description
1.3.2
High-speed Outputs
The M21208/M21218 output buffer is an open collector buffer that is designed for typical return loss of 15dB using
standard through-hole BNC connectors as typically employed with the GS9068/GS1528 series recommended
back-termination and matching circuit as shown in Figure 1-3. The Output Return Loss (ORL) may be further
optimized by using a different output matching network or component values and may vary with PCB layout or
component selection. The output return loss of the M21208/M21218 is measured while forcing the outputs to a DC
high or low state. Under normal operating conditions, the outputs of the M21208/M21218 will not be held to a static
high or low state, so the measured output return loss will not represent the actual output return loss under normal
operating conditions. To estimate the output return loss performance under typical operating conditions, an
interpolation can be performed on the measured values for the output high condition and output low condition. The
equations used for the interpolation are as follows:
RcH = RmH - (RmH - RmL) / 4 and
RcL = RmL + (RmH - RmL) / 4
RcH = Corrected ORL with output high
RcL = Corrected ORL with output low
RmH = Measured ORL with output stuck high
RmL = Measured ORL with output stuck low
Figure 1-3. Typical Output Matching/Back-termination circuit
AV_DD
I_DD
SDO
M21208
M21218
75Ω
75Ω
SDO
4.7 nH
BNC
4.7uF
75Ω
I _{TERM 10nF}
AV _DDTERM
75Ω
BNC
4.7uF
4.7 nH
212x8-DSH-001-B
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