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MAX2023_V1

High-Dynamic-Range, Direct Up-/Downconversion 1500MHz to 2500MHz Quadrature Mod/Demod

Maxim Integrated 

High-Dynamic-Range, Direct Up-/Downconversion

1500MHz to 2500MHz Quadrature Mod/Demod

I/Q Modulator

The MAX2023 modulator is composed of a pair of

matched double-balanced passive mixers and a balun.

The I and Q differential baseband inputs accept signals

from DC to 450MHz with differential amplitudes up to

4VP-P. The wide input bandwidths allow operation of the

MAX2023 as either a direct RF modulator or as an

image-reject mixer. The wide common-mode compli-

ance range allows for direct interface with the base-

band DACs. No active buffer circuitry is required

between the baseband DACs and the MAX2023 for

wideband applications.

The I and Q signals directly modulate the 0° and 90° LO

signals and are upconverted to the RF frequency. The out-

puts of the I and Q mixers are combined through a balun

to produce a singled-ended RF output.

Applications Information

LO Input Drive

The LO input of the MAX2023 is internally matched to

50Ω, and requires a single-ended drive at a 1500MHz

to 2500MHz frequency range. An integrated balun con-

verts the singled-ended input signal to a differential sig-

nal at the LO buffer differential input. An external

DC-blocking capacitor is the only external part required

at this interface. The LO input power should be within

the -3dBm to +3dBm range. An LO input power of

0dBm is recommended for best overall peformance.

Modulator Baseband I/Q Input Drive

Drive the MAX2023 I and Q baseband inputs differen-

tially for best performance. The baseband inputs have

a 50Ω differential input impedance. The optimum

source impedance for the I and Q inputs is 100Ω differ-

ential. This source impedance achieves the optimal sig-

nal transfer to the I and Q inputs, and the optimum

output RF impedance match. The MAX2023 can accept

input power levels of up to +20dBm on the I and Q

inputs. Operation with complex waveforms, such as

CDMA carriers or GSM signals, utilize input power lev-

els that are far lower. This lower power operation is

made necessary by the high peak-to-average ratios of

these complex waveforms. The peak signals must be

kept below the compression level of the MAX2023.

The four baseband ports need some form of DC return

to establish a common mode that the on-chip circuitry

drives. This can be achieved by directly DC-coupling to

the baseband ports (staying within the ±3.5V common-

mode range), through an inductor to ground, or through

a low-value resistor to ground.

WCDMA/LTE/TD-LTE Transmitter

Applications

The MAX2023 is designed to interface directly with

Maxim high-speed DACs. This generates an ideal total

transmitter lineup, with minimal ancillary circuit elements

required for widespread applications. Such DACs

include the MAX5875 series of dual DACs, and the

MAX5895 dual interpolating DAC. These DACs have

ground-referenced differential current outputs. Typical

termination of each DAC output into a 50Ω load resistor

to ground, and a 10mA nominal DC output current

results in a 0.5V common-mode DC level into the modu-

lator I/Q inputs. The nominal signal level provided by

the DACs will be in the -12dBm range for a single

CDMA or WCDMA carrier, reducing to -18dBm per

carrier for a four-carrier application.

The I/Q input bandwidth is greater than 450MHz at

-0.5dB response. The direct connection of the DAC to

the MAX2023 ensures the maximum signal fidelity, with

no performance-limiting baseband amplifiers required.

The DAC output can be passed through a lowpass filter

to remove the image frequencies from the DAC’s output

response. The MAX5895 dual interpolating DAC can be

operated at interpolation rates up to x8. This has the ben-

efit of moving the DAC image frequencies to a very high,

remote frequency, easing the design of the baseband fil-

ters. The DAC’s output noise floor and interpolation filter

MAX5895

DUAL 16-BIT INTERP DAC 50Ω

BBI

FREQ

50Ω

I/Q GAIN AND

LO

OFFSET ADJUST

50Ω

MAX2023

RF MODULATOR

0°

90°

∑

RF

FREQ

BBQ

50Ω

Figure 1. MAX5895 DAC Interfaced with MAX2023 for

cdma2000 and WCDMA Base Stations

11

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