AND8020D datasheet(7/18 Pages) AD

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AND8020/D

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Table C. Y Term Table

|VCC−VEE| = 5.0 V

|VCC−VEE| = 3.3 V

|VCC−VEE| = 2.5 V

Rt1

Rt2

Rt3

Rt1

Rt2

Rt3

Rt1

Rt2

Rt3

112

21.2

156

29.7

166

31.8

179

33.9

201

38.1

100

223

100

42.4

120

268

120

109

120

50.8

150

335

150

136

150

63.6

VEE

Figure 7. Standard Pair with External Parallel

(*or twisted pair)

*T−Line Z0

Near DC Current Return − Standard Pair

Termination

The standard pair termination scheme uses a pull−down

resistor, RE, located at each driver pin to return the output

transistor bias current near the driver, and an impedance

matching parallel resistor, RT, located at the receiver input

pins (see Figure 7, standard pair with external parallel, and

Figure 8,

standard

pair

termination

with

internal

termination, and Figure 9, standard pair termination with

singulated internal termination resistors). The impedance

matching parallel resistor may be internal or external

depending on the receiver device. If internal to the receiver,

the resistor may be singulated or combined (“combo”) for

external pinout.

The diagram of Figure 7 shows a Standard Pair

Termination with an RE resistor for DC output current bias

located nearby each driver pin: refer to Table B, for values

of RE. The differential transmission line AC impedance

matching resistance, Rt, is located externally near the

receiver input pins.

As a variation of a Standard Pair Termination, a receiver

may provide the differential transmission line AC

impedance matching resistance, Rt, internally. This internal

impedance matching termination may be pinned out either

combined into a Combo Vt pin or each resistor may be

singulated and pinned out, such as Vt1 and Vt2.

When left open, the Combo Pin still provides a passive

100

W termination across the nearby receiver’s differential

signal line pair. This can compliment a pull−down resistor, RE,

located on each line of a differential at the driver pins. This is

illustrated in Figure 8.

Figure 8. Standard Pair Termination with

Internal Termination

Open Vt Pin

(*or twisted pair)

Driver

Receiver

*T−Line Z0

Internal Termination Combo Pin

VEE

When the Internal Termination resistors are singulated,

the two Vt pins must be shorted to create the 100

W value as

shown in Figure 9.

Figure 9. Standard Pair Termination with

Singulated Internal Termination Resistors

Internal Termination Singulated Pins

(*or twisted pair)

Driver

Receiver

*T−Line Z0

VEE

Vt1

Vt2

Shorted

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