AD8010

–10–

REV. A

Differential Line Driver

Twisted pair transmission lines are more often being used for

high frequency analog and digital signals. Over long distances,

however, the attenuation characteristics of these lines can

degrade the performance of the transmission system. To com-

pensate for this, larger signals are transmitted, which after the

attenuation, will still have useful signal strength.

The high output current of two AD8010s can be used along

with a transformer to create a high power differential line driver.

The differential configuration effectively doubles the output

swing, while the step-up transformer further increases the out-

put voltage.

In the circuit in Figure 31 the A device is configured as a gain-

of-two follower, while the B device is a gain-of-two inverter.

These will produce a differential output signal whose maximum

value is twice the peak-to-peak value of the maximum output of

one device. For this circuit a 12 V peak-to-peak output can be

obtained.

The op amps drive a 1:2 step-up transformer that drives a

100

Ω transmission line. Since the impedance reflected back to

the primary varies as the square of the turns ratio, it will appear

as 25

Ω at the primary. This source terminating resistor is split

as a 12.4

Ω resistor at the output of each device.

The circuit shown is capable of delivering 12 V p-p to the line

and operates with a –3 dB bandwidth of 40 MHz. The peak

current output of either op amp is 100 mA.

Figure 31. High Output Differential Line Driver Using Two AD8010s.

NOTE: Please see Figure 29 for Recommended Bypassing Technique.

AD8010

499

499

150

402

AD8010

150

806

12.4

12.4

+6

–6

1:2

100