AD8340 datasheet(12/20 Pages) AD

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AD8340

Data Sheet

APPLICATIONS INFORMATION

USING THE AD8340

The AD8340 is designed to operate in a 50 Ω impedance

system. Figure 30 illustrates where the RF input is driven in

a single-ended fashion while the differential RF output is

converted to a single-ended output with an RF balun. The

baseband controls for the I and Q channels are typically driven

from differential DAC outputs. The power supplies, VPRF and

VPS2, should be bypassed appropriately with 0.1 µF and 100 pF

capacitors. Low inductance grounding of the CMOP and CMRF

common pins is essential to prevent unintentional peaking of

the gain.

RF INPUT AND MATCHING

The input impedance of the AD8340 is defined by the characteris-

tics of the polyphase network. The capacitive component of the

network causes its impedance to roll off with frequency, albeit at

a slower rate than 6 dB/octave. With matching inductors on the

order of 5.6 nH in series with each of the RF inputs, RFIP and

RFIM, a 50 Ω match is achieved with a return loss of >10 dB

over the operating frequency range. Different matching

inductors can improve matching over a narrower frequency

range. The single-ended and differential input impedances are

exactly the same.

50Ω

100pF

RFIM

RFIP

PHASE

5.6nH

100pF 5.6nH

~1VDC

Figure 29. RF Input Interface to the AD8340 Showing

Coupling Capacitors and Matching Inductors

The RFIP and RFIM should be ac-coupled through low loss

series capacitors as shown in Figure 29. The internal dc levels

are at approximately 1 V. For single-ended operation, one input

is driven by the RF signal and the other input is ac grounded.

DSOP

VPS2

VPRF

CMRF

RFIM

RFIP

CMOP

RFOM

RFOP

QFLP

CMOP

CMRF

VPRF

IFLP

AD8340

C12

(SEE TEXT)

C11

(SEE TEXT)

0.1µF

5.6nH

100pF

5.6nH

100pF

IBBM

IBBP

INPUT

QBBP

QBBM

120nH

C14

0.1µF

C10

0.1µF

C18

100pF

C17

100pF

ETC1-1-13

OUTPUT

DISABLE

0.1µF

100pF

Figure 30. Basic Connections

Rev. C | Page 12 of 20

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