ADL5565ACPZ-R7 datasheet(20/28 Pages) AD

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ADL5565

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ADC INTERFACING

The ADL5565 is a high output linearity amplifier that is optimized

for ADC interfacing. There are several options available to the

designer when using the ADL5565. Figure 40 uses a wideband

1:1 transmission line balun followed by two 40 Ω resistors in

parallel with the three input impedances (which change with

the gain selection of the ADL5565) to provide a 50 Ω differential

impedance and provides a wideband match to a 50 Ω source.

The ADL5565 is ac-coupled from the AD9467 to avoid common-

mode dc loading. The 33 Ω resistors improve the isolation between

the ADL5565 and any switching currents present at the analog-

to-digital, sample-and-hold circuitry. The AD9467 input presents a

530 Ω differential load impedance and requires a 2 V to 2.5 V

differential input swing to reach full scale (VREF = 1 V to 1.25 V).

This circuit provides variable gain, isolation, and source

matching for the AD9467.

Applying a full-scale, single-tone signal from the ADL5565, an

SFDR of 89.2 dBc is realized (see Figure 37). Applying two half-

scale signals from the ADL5565 in a gain of 6 dB, an SFDR of

87.5 dBc is achieved at 100 MHz (see Figure 38). The bandwidth

of the circuit in Figure 40 is shown in Figure 39.

105

120

GAIN = 6dB

SNR = 69.44dBc

SFDR = 89.2dBc

SECOND = –85.1dBc

THIRD = –89.3dBc

NOISE FLOOR = –115.7dB

FREQUENCY (MHz)

–15

–30

–45

–60

–75

–90

–105

–120

–135

–150

Figure 37. Measured Single-Tone Performance of the

Circuit in Figure 40 for a 100 MHz Input Signal

3045607590

105

120

FUNDAMENTAL1 = –7.078dBFS

FUNDAMENTAL2 = –7.169dBFS

IMD (2f1 – f2) = –88.237dBc

IMD (2f2 + f1) = –91.37dBc

NOISE FLOOR = –115.96dB

FREQUENCY (MHz)

–15

–30

–45

–60

–75

–90

–105

–120

–135

–150

2F2 – 2F1

F1 – F2

F2 – F1

2F1 – F2

2F2 – F1

2F1 – 2F2

Figure 38. Measured Two-Tone Performance of the Circuit in Figure 40 for a

100 MHz Input Signal

–

0100

200

300

400

500

FREQUENCY (MHz)

Figure 39. Measured Frequency Response of the Wideband

ADC Interface Depicted in Figure 40

The wideband frequency response is an advantage in broad-

band applications, such as predistortion receiver designs and

instrumentation applications. However, by designing for a wide

analog input frequency range, the cascaded SNR performance is

somewhat degraded due to high frequency noise aliasing into

the wanted Nyquist zone.

0.1µF

40Ω

50Ω

0.1

µF

ETC1-1-13

VIN1

VIP1

VIP2

VIN2

40Ω

ADL5565

0.1µF

33Ω

VOP

VON

33Ω

AD9467

16-BIT ADC

VIN+

VIN–

Figure 40. Wideband ADC Interfacing Example Featuring the AD9467

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