ADF4602 datasheet(17/36 Pages) AD

17 / 36 page

ADF4602

Rev. 0 | Page 17 of 36

THEORY OF OPERATION

TRANSMITTER DESCRIPTION

TXBBI

TXBBIB

TXBBQ

TXBBQB

GAIN CONTROL

TXPWR_SET[11:0]

–90 DEGREES

÷2

TXBs

TESTQ, SWAP_Q

TESTI, SWAP_I

LPF

OUTPUT

LB ONLY

DIVIDER

DIVIDER AND

QUAD GEN

INTEGRATED

BALUN

Figure 35. Transmitter Block Diagram

The ADF4602 contains a highly innovative low noise variable

gain direct conversion transmitter architecture, that removes the

need for external transmit SAW filters. The direct conversion

architecture significantly reduces the risk of transmit harmonics

across all bands due to the simplified nature of the frequency

plan. See Figure 35 for a block diagram.

I/Q Baseband

The baseband interface for the I and Q channels is a differential,

dc-coupled input, supporting a wide range of input common-

mode voltages (VCM). The allowable input common-mode range is

1.05 V to 1.4 V. The maximum signal swing allowed is 550 mV

peak differential. This corresponds to a 1.1 V peak-to-peak

differential on either the I or Q channel. Figure 36 shows a

graphical definition of peak differential voltage and VCM.

The baseband input signals pass through a second order

Butterworth filter prior to the quadrature modulator. The cutoff

frequency is 4 MHz. This gives some rejection of the DAC

images. The filter also helps to suppress any spurious signals

that might be coupled to the baseband terminals on

the PCB.

For ease of PCB routing between the ADF4602 and the transmit

DAC, the I and Q differential inputs can be internally swapped.

For user test purposes, the I and Q inputs can also be internally

shorted together and a dc offset applied. This produces a large

carrier at the RF output, which is useful for signal path integrity

testing.

VCM

I OR Q

IB OR QB

PEAK V DIF

VOLTS

TIME

Figure 36. Transmit Baseband Input Signals

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