ADL5535

Rev. 0 | Page 12 of 16

ADC DRIVING APPLICATION

The ADL5535 is a high linearity, fixed gain IF amplifier suitable

for use as an ADC driver. Figure 22 shows the schematic of the

ADL5535 driving the AD9268 16-bit analog-to-digital converter

(ADC). The ADL5535 has a single-ended input and output imped-

ance of 50 Ω. A 1:1 impedance transformer, along with termination

resistors and series ferrite beads, are used to present a 50 Ω load

for the antialiasing filter interface. The filter interface between the

ADL5535 and the AD9268 is a sixth-order Butterworth low-pass

filter. The interface provides a 50 MHz, 1 dB bandwidth centered

around 175 MHz. Following the sixth-order filter, a shunt LC tank

circuit was inserted to further reduce the low frequency response

of the filter, giving more of a band-pass response to the filter.

The normalized wideband response is shown in Figure 19.

–45

–40

–35

–30

–25

–20

–15

–10

–5

0

5

0

50

100

150

200

250

300

350

400

FREQUENCY (MHz)

Figure 19. Normalized Response of the ADC Interface Shown

in Figure 22

FREQUENCY (MHz)

60

54

48

42

36

30

24

18

12

06

0

–15

–30

–45

–75

–90

–60

–105

–120

–135

SAMPLE FREQUENCY = 122.88MHz

SNRFS = 75.877dB

INPUT FREQUENCY = 170MHz

FUNDAMENTAL POWER = –1.044dBFS

SECOND HARMONIC POWER = –75.499dBc

THIRD HARMONIC POWER = –80.003dBc

NOISE FLOOR = –153.762dBFS/√Hz

5

3

2

6

4

+

Figure 20. Measured Single-Tone Performance of the Circuit Shown

in Figure 22

FREQUENCY (MHz)

60

54

48

42

36

30

24

18

12

06

0

–15

–30

–45

–75

–90

–60

–105

–120

–135

FUNDAMENTAL1 = –7.161dBFS

FUNDAMENTAL2 = –7.116dBFS

IMD (2f1 – f2) = –66.07dBc

IMD (2f2 – f1) = –67.588dBc

NOISE FLOOR = –150.84dBFS/√Hz

f2 – f1

f1 + f2

2f1 – f2

2f2 – f1

Figure 21. Measured Two-Tone Performance of the Circuit Shown

in Figure 22

1

33Ω

33Ω

66Ω

66Ω

22pF

22nH

56nH

8pF

27pF

100pF

470nH

5V

50Ω

VCM

VCM

ADL5535

68nH

8.2pF

72nH

MABA-007159-000000

FERRITE BEAD

10Ω AT 100MHz

0.1µF

0.1µF

FERRITE BEAD

10Ω AT 100MHz

AD9268

VIN+A

VIN–A

Figure 22. Schematic of the ADL5535 Driving the AD9268 16-Bit ADC