13

®

OPA623

APPLICATIONS INFORMATION

The precise pulse response and high slew rate enables the

OPA623 to be used in digital communication systems.

Figure 12 shows the circuit schematic of an output amplifier

with a gain of +2V/V, which can drive a 75

Ω coaxial cable

with a high-speed data stream of 140Mbit/s. Figure 13, for

a binary 0, and Figure 14, for a binary 1, shows the pulse

masks of the CCITT recommendation G.703 and the corre-

sponding pulse responses of the OPA623. The signal code at

the file rate of 139.264Mbit/s is CMI, the signal amplitude

is 1Vp-p with

±11dB amplitude limits. Naturally, the OPA623

can also be used for HDB3 encoded 34Mbit/s,155Mbit/s,

STM-1, and 155Mbit/s B-ISDN transmission systems.

FIGURE 12. Driver Amplifier for a Digital 140Mbit/s

Transmission system.

FIGURE 13. Mask of a Pulse Corresponding to a Binary 0 per CCITT Recommendation G.703.

0.60

0.55

0.50

0.45

0.40

0.05

–0.05

–0.40

–0.45

–0.50

–0.55

–0.60

V

1ns

0.1ns

0.1ns

Nominal

= Note 1.

Negative

transitions

Positive transition

at mid-unit interval

1ns

1ns

1ns

1.795ns

1.795ns

T = 7.18ns

1.795ns

1ns

1ns

1.795ns

Nominal

Pulse

0.1ns

0.1ns

0.35ns

0.35ns

NOTE: (1) The maximum “steady state” amplitude should not exceed the 0.55V limit. Overshoots and other transients are permitted to fall

into the dotted area, bounded by the amplitude levels 0.55V and 0.6V, provided that they do not exceed the steady state level by more

than 0.05V. The possibility of relaxing the amount by which the overshoot may exceed the steady state level is under study.

(2) For all measurements using these masks, the signal should be AC coupled, using a capacitor of not less than 0.01µF, to the input of

the oscilloscope used for measurements.

The nominal zero level for both masks should be aligned with the oscilloscope trace with no input signal. With the signal then applied, the

vertical position of the trace can be adjusted with the objective of meeting the limits of the masks. Any such adjustment should be the

same for both masks and should not exceed

±0.05V. This may be checked by removing the input signal again and verifying that the trace

lies within

±0.05V of the nominal zero level of masks.

(3) Each pulse in a coded pulse sequence should meet the limits of the relevant mask, irrespective of the state of the preceding and

succeeding pulses. For actual verification, if a 139264kHz timing signal associated with the source of the interface signal is available, its

use as a timing reference for an oscilloscope is preferred. Otherwise, compliance with the relevant mask may be tested by means of all-0s

and all-1s signals, respectively. (In practice, the signal may contain frame alignment bits per Rec. G.751.)

(4) For the purpose of these masks, the rise time and decay time should be measured between –0.4V and 0.4V, and should not exceed

2ns.

OPA623

R

2

R

1

300

Ω

R

IN

6

V

OUT

300

Ω

180

Ω

–V

CC

+V

CC

4

7

2

3

–In

+In

V

IN

G = 1 + R