THS4513 datasheet(27/34 Pages) TI

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VS+

VSignal

VS-

VOUT+

VOUT-

THS 4513

VS+

RPU

2.5 V

348 W

340 W

56.2 W

25 W

56.2 W

50 W

THS4513

0.22 f

To 50

Test

Equipment

0.1 f

-2.5 V

1:1

6.8 pf

OUT

0.22 f

50-W

Single-

Ended

AC-Coupled

Source

V S+= 3V to 5V

V Signal

V S-

R F

R G

R T

R O

V OUT+

V OUT-

THS

R S

R T

R S

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0.1

100

1000

f - Frequency (MHz)

Low Pass Filter

THS4513 + ADS5500 Combined Performance

THS4513

SLOS472 – AUGUST 2005

Figure 80. THS4513 DC Coupled Single-Supply

with RPU Used to Set VIC

Figure 82. 60-MHz Low-Pass Filter

Figure 81 shows AC coupling to the source. Using

capacitors in series with the termination resistors

allows the amplifier to self-bias both input and output

to mid-supply.

Figure 81. THS4513 AC Coupled Single-Supply

Figure 83. Low-Pass Filter Measured

Frequency Response

One application for the THS4513 is as a unity-gain

buffer with low-pass filtering. Figure 82 shows a

circuit that is driven by an AC-coupled 50-

Ω source. A

The THS4513 is designed to be a high performance

1:1 transformer converts the differential output of the

drive amplifier for high performance data converters

THS4513 into a single-ended output capable of

like the ADS5500 14-bit 125-MSPS ADC. Figure 84

driving 50-

Ω test equipment. The circuit as shown

shows a circuit combining the two devices. The

has an overall gain of -6dB due to the voltage divider

THS4513 amplifier circuit provides 10 dB of gain,

on the device output, and has a roll-off frequency of

converts the single-ended input to differential, and

approximately 60 MHz. The measured gain versus

sets the proper input common-mode voltage to the

frequency response of the overall circuit is shown in

ADS5500. The 100-

Ω resistors and 2.7-pF capacitor

Figure 83. The low-frequency roll-off is due to losses

between the THS4513 outputs and ADS5500 inputs

in the output transformer at those frequencies.

along with the input capacitance of the ADS5500 limit

the bandwidth of the signal to 115 MHz (–3 dB). For

testing, a signal generator is used for the signal

source. The generator is an AC-coupled 50-

Ω source.

A band-pass filter is inserted in series with the input

to reduce harmonics and noise from the signal

source. Input termination is accomplished via the

69.8-

Ω resistor and 0.22-µF capacitor to ground in

conjunction with the input impedance of the amplifier

circuit. A 0.22-µF capacitor and 49.9-

Ω resistor is

THS4513 Datasheet(PDF) 27 Page - Texas Instruments

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