THS4513 datasheet(21/31 Pages) TI

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APPLICATION INFORMATION

APPLICATIONS

Differential Input to Differential Output Amplifier

Single-Ended

Input

THS 4513

Differential

Output

OUT+

OUT–

–

Input Common-Mode Voltage Range

OUT+

OUT–

S+

IN–

S–

IN+

THS4513

Differential

Input

Differential

Output

–

OUT

(1)

Single-Ended Input to Differential Output

Setting the Output Common-Mode Voltage

THS4513-SP

SLOS539A – SEPTEMBER 2007 – REVISED OCTOBER 2007

The following circuits show application information for

the THS4513. For simplicity, power supply decoupling

capacitors are not shown in these diagrams. Please

see the THS4513 EVM section for recommendations.

For more detail on the use and operation of fully

differential op amps refer to

application

report

Fully-Differential Amplifiers (SLOA054) .

The THS4513 is a fully differential op amp and can

be used to amplify differential input signals to

Figure 61. Single-Ended Input to Differential

differential output signals. A basic block diagram of

Output Amplifier

the circuit is shown in Figure 60 (CM input not

shown). The gain of the circuit is set by RF divided by

RG.

The input common-mode voltage of a fully differential

op amp is the voltage at the '+' and '–' input pins of

the op amp.

It is important to not violate the input common-mode

voltage range (VICR) of the op amp. Assuming the op

amp is in linear operation, the voltage across the

input pins is only a few millivolts at most. So finding

the voltage at one input pin will determine the input

common-mode voltage of the op amp.

Treating the negative input as a summing node, the

voltage is given by Equation 1:

Figure 60. Differential Input to Differential Output

To determine the VICR of the op amp, the voltage at

Amplifier

the negative input is evaluated at the extremes of

VOUT+.

Depending on the source and load, input and output

termination can be accomplished by adding RIT and

As the gain of the op amp increases, the input

RO.

common-mode voltage becomes closer and closer to

the input common-mode voltage of the source.

Amplifier

The THS4513 can be used to amplify and convert

The output common-mode voltage is set by the

single-ended

input

signals

differential

output

voltage at the CM pin(s). The internal common-mode

signals. A basic block diagram of the circuit is shown

control circuit maintains the output common-mode

in Figure 61 (CM input not shown). The gain of the

voltage within 3 mV offset (typ) from the set voltage,

circuit is again set by RF divided by RG.

when set within 0.5 V of mid-supply, with less than

4 mV differential offset voltage. If left unconnected,

the common-mode set point is set to mid-supply by

internal circuitry, which may be over-driven from an

external source. Figure 62 is representative of the

CM input. The internal CM circuit has about 700 MHz

of –3 dB bandwidth, which is required for best

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