AD8340(2004) Просмотр технического описания (PDF) - Analog Devices

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AD8340
(Rev.:2004)

700 MHz to 1000 MHz RF Vector Modulator

Analog Devices 

AD8340

APPLICATIONS

USING THE AD8340

The AD8340 is designed to operate in a 50 Ω impedance

system. Figure 30 illustrates an example where the RF input is

driven in a single-ended fashion while the differential RF out-

put is converted to a single-ended output with a 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 charac-

teristics 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. By using 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.

100pF 5.6nH

100pF 5.6nH

RF

50Ω

RFIM

~1VDC

RC

PHASE

RFIP

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 while the other input is ac grounded.

VP

IBBM

IBBP

VP

RF

INPUT

VP

QBBP

QBBM

C2

100pF

C12

(SEE TEXT)

C8

0.1µF

C7

100pF

IFLP

VPRF

C6

L3

100pF 5.6nH

CMRF

RFIM

C5

100pF

L4

5.6nH

RFIP

CMRF

C3

0.1µF

C4

100pF

VPRF

QFLP

AD8340

C11

(SEE TEXT)

C1

0.1µF

DSOP

CMOP

CMOP

RFOM

RFOP

CMOP

CMOP

VPS2

C10

0.1µF

C9

100pF

VP

A

OUTPUT

DISABLE

B

C17

100pF ETC1-1-13

L1

120nH

C18

L2

100pF

120nH

C14

0.1µF

VP

Figure 30. Basic Connections

RF

OUTPUT

Rev. 0 | Page 12 of 20

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