THS4140, THS4141

HIGHSPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

SLOS320E − MAY 2000 − REVISED JANUARY 2004

13

POST OFFICE BOX 655303

APPLICATION INFORMATION

data converters (continued)

Some single supply applications may require the input voltage to exceed the common-mode input voltage

range. In such cases, the following circuit configuration is suggested to bring the common-mode input voltage

within the specifications of the amplifier.

VIN

−

+

−

+

DVDD

VOCM

AVSS

AVDD

AIN

AIN

VDD

Vref

5 V

VCC

0.1

µF

VCC

RPU

VCC

RPU

Rg

Rg

VP

Rf

Rf

VOUT

VOUT

Figure 24. Circuit With Improved Common-Mode Input Voltage

R

PU +

V

P

–V

CC

V

IN

–V

P

1

RG

) V

OUT

–V

P

1

RF

driving a capacitive load

Driving capacitive loads with high-performance amplifiers is not a problem as long as certain precautions are

taken. The first is to realize that the THS414x has been internally compensated to maximize its bandwidth and

slew rate performance. When the amplifier is compensated in this manner, capacitive loading directly on the

output will decrease the device’s phase margin leading to high-frequency ringing or oscillations. Therefore, for

capacitive loads of greater than 10 pF, it is recommended that a resistor be placed in series with the output of

the amplifier, as shown in Figure 25. A minimum value of 20

Ω should work well for most applications. For

example, in 50-

Ω transmission systems, setting the series resistor value to 50 Ω both isolates any capacitance

loading and provides the proper line impedance matching at the source end.

THS414x

Output

Output

20

Ω

20

Ω

390

Ω

390

Ω

390

Ω

390

Ω

Figure 25. Driving a Capacitive Load