AD8352

Rev. B | Page 15 of 20

AD8352

50Ω

0Ω

0Ω

0.1µF

0.1µF

0.1µF

0.1µF

16

1

2

3

4

5

24Ω

0.1µF

10

24Ω

0.1µF

11

8, 13

14

AD9445

IF/RF INPUT

ADT1-1WT

FREQUENCY (MHz)

0

–150

052.50

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

–130

–140

5.25 10.50 15.75 21.00 26.25 31.50 36.75 42.00 47.25

SNR = 61.98dBc

NOISE FLOOR = –111.2dB

FUND1 = –7.072dBFS

FUND2 = –7.043dBFS

IMD (2F2-F1) = –89dBc

IMD (2F1-F2) = –88dBc

Figure 34. Differential Input to the AD8352 Driving the AD9445

25Ω

50Ω

50Ω

AD8352

33Ω

33Ω

0.1µF

0.1µF

0.1µF

0.1µF

AC

VIP

VIN

VOP

VON

200Ω

AD9445

VIN+

VIN–

Figure 37. Two Tone Distortion AD8352 Driving AD9445,

Analog In = 98 MHz and 101 MHz, See Figure 34

LAYOUT AND TRANSMISSION LINE EFFECTS

High Q inductive drives and loads, as well as stray transmission

line capacitance in combination with package parasitics, can

potentially form a resonant circuit at high frequencies resulting

in excessive gain peaking or possible oscillation. If RF transmission

lines connecting the input or output are used, they should be

designed such that stray capacitance at the input/output pins is

minimized. In many board designs, the signal trace widths should

be minimal where the driver/ receiver is more than one-eighth

of the wavelength from the AD8352. This nontransmission line

configuration requires that underlying and adjacent ground and

low impedance planes be dropped from the signal lines. In a

similar fashion, stray capacitance should be minimized near the

requires not placing low impedance planes near these components.

Refer to the evaluation board layout (Figure 39 and Figure 40)

for more information. Excessive stray capacitance at these nodes

results in unwanted high frequency distortion. The 0.1 μF supply

decoupling capacitors need to be close to the amplifier. This

includes Signal Capacitor C2 through Signal Capacitor C5.

Figure 35. Single-Ended Input to the AD8352 Driving the AD9445

0

–150

0

52.50

FREQUENCY (MHz)

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

–130

–140

5.25 10.50 15.75 21.00 26.25 31.50 36.75 42.00 47.25

SNR = 67.26dBc

SFDR = 83.18dBc

NOISE FLOOR = –110.5dB

FUND = –1.074dBFS

SECOND = –83.14dBc

THIRD = –85.39dBc

Figure 36. Single Tone Distortion AD8352 Driving AD9445,

Parasitic suppressing resistors (R5, R6, R7, and R11) can be

used at the device input/output pins. Use 25 Ω series resistors

(Size 0402) to adequately de-Q the input and output system

from most parasitics without a significant decrease in gain. In

general, if proper board layout techniques are used, the suppression

resistors are not necessarily required. Output Parasitic Suppression

Resistor R7 and Output Parasitic Suppression Resistor R11 can

be required for driving some switch capacitor ADCs. These

suppressors, with Input C of the converter (and possibly added

External Shunt C), help provide charge kickback isolation and

improve overall distortion at high encode rates.