MAX2021 datasheet(13/20 Pages) MAXIM

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MAX2021

High-Dynamic-Range, Direct Up-/Downconversion

650MHz to 1200MHz Quadrature Mod/Demod

Maxim Integrated

The I/Q input power levels and the insertion loss of the

device determine the RF output power level. The input

power is a function of the delivered input I and Q volt-

ages to the internal 50Ω termination. For simple sinu-

soidal baseband signals, a level of 89mVP-P differential

on the I and the Q inputs results in a -17dBm input

power level delivered to the I and Q internal 50Ω termi-

nations. This results in an RF output power of -23.2dBm.

External Diplexer

LO leakage at the RF port can be nulled to a level less

than -80dBm by introducing DC offsets at the I and Q

ports. However, this null at the RF port can be compro-

mised by an improperly terminated I/Q IF interface. Care

must be taken to match the I/Q ports to the driving DAC

circuitry. Without matching, the LO’s second-order (2fLO)

term may leak back into the modulator’s I/Q input port

where it can mix with the internal LO signal to produce

additional LO leakage at the RF output. This leakage

effectively counteracts against the LO nulling. In addi-

tion, the LO signal reflected at the I/Q IF port produces a

residual DC term that can disturb the nulling condition.

As demonstrated in Figure 2, providing an RC termina-

tion on each of the I+, I-, Q+, Q- ports reduces the

amount of LO leakage present at the RF port under

RF-MODULATOR

100Ω

L = 40nH

C = 6.8pF

∑

L = 40nH

100Ω

C = 6.8pF

0°

90°

MAX2021

Figure 2. Diplexer Network Recommended for GSM 900

Transmitter Applications

DAC

50I

31dB

17dB

RFOUT

50I

DAC

50I

MAX2021

MAX5873

DUAL DAC

45, 80,

95MHz

LOOPBACK

OUT

(FEEDS BACK

INTO Rx CHAIN

FRONT END)

Rx OFF

SPI

CONTROL

SPI

LOGIC

MAX2058

RF DIGITAL VGA

MAX9491

VCO + SYNTH

Figure 1. Transmitter Lineup

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