M21418/M21428

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8

HD/SD and 3G/HD/SD-SDI Cable Drivers

Rev V6

1.2.2

High-speed Outputs

The M21418/M21428 output buffer is an open collector buffer that is designed for a return loss of 15 dB at SD and

HD rates and 10 dB at 3G rates, using standard through-hole BNC connectors as typically employed in broadcast

video equipment. A typical output matching circuit is shown in Figure 1-3. The Output Return Loss (ORL) is

dependent on many factors such as the value and type of components used, PCB layout, PCB trace lengths, and

type of PCB di-electric, therefore, the recommendations in the figure below should be used as starting guidelines

only. Different output matching network topologies and different component values will result in different ORL

performance.

The M21418/M21428 has SD-SDI and HD-SDI rise/fall times that are typically faster than the legacy cable driver

devices but within the relevant SMPTE specification for additional margin in most designs. The faster output slew

rate results in a more open eye. The actual maximum output of the part depends on the applied IC voltage as well

as the external termination voltage for the load termination. The limitations are discussed in Section 1.1.

Figure 1-3.

Output Matching/Back-termination Circuit (Both Outputs Used)

M21418

M21428

SDO

SDO

AVDD

I DD

75 Ω

75 Ω

I TERM

10 nF

DDTERM

AV

4.7 nH

75 Ω

4.7 uF

BNC

4.7 nH

75 Ω

4.7 uF

BNC