AD8150AST datasheet(18/35 Pages) AD

18 / 35 page

AD8150

–18–

REV. 0

VCC

VEE

DISABLE

IOUT

OUTyyP

OUTyyN

VCC – 2V

VEE

Figure 33. Simpliﬁed Output Circuit

To ensure proper operation, all outputs (including unused output)

must be pulled high using external pull-up networks to a level

within the output compliance range. If outputs from multiple

AD8150s are wired together, a single pull-up network may be

used for each output bus. The pull-up network should be chosen

to keep the output voltage levels within the output compliance

range at all times. Recommended pull-up networks to produce

PECL/ECL 100K and 10K compatible outputs are shown in

Figure 34. Alternatively, a separate supply can be used to pro-

vide VCOM; making RCOM and DCOM unnecessary.

VCC

RCOM

VCOM

OUTyyN

OUTyyP

AD8150

VCC

DCOM

VCOM

OUTyyN

OUTyyP

AD8150

Figure 34. Output Pull-Up Networks: a) ECL 100K,

b) ECL 10K

The output levels are simply:

VOH = VCOM

VOL = VCOM – IOUTRL

VSWING = VOH – VOL = IOUTRL

VCOM = VCC – IOUTRCOM (100K Mode)

VCOM = VCC – V (DCOM) (10K Mode)

The common-mode adjustment element (RCOM or DCOM) may

be omitted if the input range of the receiver includes the positive

supply voltage. The bypass capacitors reduce common-mode

perturbations by providing an ac short from the common nodes

(VCOM) to ground.

When busing together the outputs of multiple AD8150s or when

running at high data rates, double termination of its outputs is

recommended to mitigate the impact of reflections due to open

transmission line stubs and the lumped capacitance of the

AD8150 output pins. A possible connection is shown in Figure

35; the bypass capacitors provide an ac short from the common

nodes of the termination resistors to ground. To maintain signal

ﬁdelity at high data rates, the stubs connecting the output pins

to the output transmission lines or load resistors should be as

short as possible.

VCC

OUTyyN

OUTyyP

OUTyyN

OUTyyP

AD8150

VCOM

RCOM

RECEIVER

Figure 35. Double Termination of AD8150 Outputs

In this case, the output levels are:

VOH = VCOM – (1/4) IOUTRL

VOL = VCOM – (3/4) IOUTRL

VSWING = VOH – VOL = (1/2) IOUTRL

Output Current Set Pin (REF)

A simpliﬁed schematic of the reference circuit is shown in Fig-

ure 36. A single external resistor connected between the REF

pin and VEE determines the output current for all output stages.

This feature allows a choice of pull-up networks and transmission

line characteristic impedances while still achieving a nominal

output swing of 800 mV. At low data rates, substantial power

savings can be achieved by using lower output swings and higher

load resistances.

AD8150

VEE

RSET

REF

VCC

IOUT/25

1.25V

Figure 36. Simpliﬁed Reference Circuit

The resistor value current is given by the following expression:

SET

OUT

Example:

RSET = 1.54 k

Ω for IOUT = 16.2 mA

The minimum set resistor is RSET,min = 1 k

Ω resulting in I

OUT,max =

25 mA. The maximum set resistor is RSET,max = 5 k

Ω result-

ing in IOUT,min = 5 mA. Nominal 800 mV output swings can be

achieved in a 50

Ω load using R

SET = 1.56 k

Ω (I

OUT = 16.2 mA)

or in a doubly-terminated 75

Ω load using RSET = 1.17 kΩ (IOUT

= 21.3 mA).

To minimize stray capacitance and avoid the pickup of unwanted

signals, the external set resistor should be located close to the

REF pin. Bypassing the set resistor is not recommended.

AD8150AST датащи(PDF) 18 Page - Analog Devices

AD8150AST датащи(HTML) 18 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

датащи скачать

ссылки URL