MT-075

terminated twisted pair for the best common-mode rejection.

A number of triple drivers are available for driving RGB signals over CAT-5 cable such as the

AD8133, AD8134, AD8146, AD8147, AD8148.

Corresponding triple receivers are also available, including the AD8143 and AD8145. The

AD8123 (Triple) and AD8128 (Single) receivers also include adjustable line equalization.

APPLICATION EXAMPLE: ADA4937-1 DIFFERENTIAL AMPLIFIER DRIVING

AD6645 14-bit 80/105MSPS ADC

The AD813x and ADA493x family of differential drivers are suitable for use in dc or ac coupled

applications with voltage gains of 1 to 4 (0 dB to 12 dB) and frequencies up to about 100 MHz

(depending on the particular member of the family). They are especially useful as low distortion

feature can be used to level shift bipolar signals to match the common-mode input voltage of the

ADC. Details of the circuit analysis of dc drivers and selection of resistor values is given in MT-

xxx. The ADIsimDiffAmp design tool, is also available to facilitate these designs.

The ADA4937-1 is one of the latest in the series of differential amplifiers and is optimized for

operation on a single +5 V supply. Figure 5 shows it is used as a level shifter to drive the

AD6645 14-bit 80/105 MSPS ADC. (The ADA4939-1 is a similar part optimized for voltage

gains ≥ 2).

103

+

–

AD6645

14-BIT ADC

A

IN–

V

IN

+155mV

± 1.1V

61.5

Ω

200

Ω

207

Ω

207

Ω

228

Ω

24.9

Ω

24.9

Ω

+2.4V

V

OCM

ADA4937-1

0.1µF

0.1µF

0.1µF

+1.3V + / – 0.275V

+2.4V – / + 0.55V

+2.4V + / – 0.55V

2.2V p-p

Differential

Input Span

+5V

f

80/105MSPS

5nV/

AD6645 SPECS:

INPUT BW = 270MHz

1 LSB = 134µV

SNR = 75dB

5nV/

√Hz

OUTPUT NOISE =

OUTPUT SNR = 20 log

0.778

= 77.6dB

+5V

C

~

50

Ω

±2.2V

Figure 5: ADA4937-1 Driving AD6645 in +5 V DC-Coupled Application

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