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MAX2402EAP

800MHz to 1000MHz Transmitter

Maxim Integrated 

800MHz to 1000MHz Transmitter

_____________________Pin Description

PIN

NAME

1

VGC

2

3, 5, 8,

13, 15, 17,

18, 20

MOD

GND

4, 12, 19 VCC

6

LO+

7

LO-

9

SHDN

10

BADJ

11

14, 16

LGND

OUT

FUNCTION

Variable Gain Control Input.

Connect to VCC for maximum gain.

Baseband Modulation Input to mixer

Ground

Supply Voltage, set between 4.75V

and 5.5V

Local-Oscillator Positive Input

Local-Oscillator Negative Input

Shutdown Control Input.

Low level = off, high level = on.

Bias Adjustment Control for power

amplifier. Connect resistor from

BADJ to V+ or GND (see Table 1).

Connect 27nH inductor from LGND

to GND to maximize output power.

Power-Amplifier Output

_______________Detailed Description

The MAX2402 transmitter is a versatile design that inte-

grates several RF functions on a single IC. It has a wide

variety of applications in portable and stationary wire-

less designs. Each of the functional blocks (shown in

the Functional Diagram) is described in detail in the fol-

lowing sections.

LO Inputs

The LO inputs are internally capacitively coupled and

self biasing. The LO port can be driven differentially or

single ended. When terminated at the LO inputs with

50Ω, the transmitter will provide full output power for LO

inputs from -6dBm to +6dBm with single-ended drive,

and -12dBm to +6dBm with differential drive. Input

power beyond this range may saturate the LO input

buffer, while input power below this range may result in

less output power. The limiter is two cascaded differen-

tial stages, which also isolates the LO input from the

mixer. This will help reduce any frequency-pulling

effects in an external LO due to mixer loading. The lim-

iter output drives one port of a double-balanced Gilbert

mixer.

MOD Input

The mixer’s other port, the MOD input, remains linear

over a 2V range from about 1.5V to 3.5V at the input.

When driven with digital modulation (0V to 5V), this port

will completely limit, resulting in a hard BPSK-

modulated signal. Since this input is self biasing, carrier

suppression can be improved by externally capacitively

coupling the signal into the port (the MOD input resis-

tance is approximately 10kΩ). This would compensate

for voltage offset or duty-cycle offset at this port, thus

increasing carrier suppression. This MOD self bias is

designed for very low on-chip offset, resulting in excel-

lent carrier suppression. Since this port self biases

when the signal is removed from MOD, the mixer will

attenuate the output power by about 40dB, resulting in

further attenuation past that attained from VGC con-

trol—a useful feature for ASK modulation.

VGC Stage

The mixer output drives the VGC stage. This stage

attenuates through a multiplication technique that does

not distort the signal with increased attenuation. VGC

control is nonattenuating when connected to the VCC

supply. VGC will attenuate for voltages from 2.5V to

1.0V. Most attenuation occurs between 1V and 2V.

Maximum attenuation is achieved below 0.8V. Typical

maximum attenuation is 40dB. At or beyond 40dB of

attenuation, the signal may be slightly nonmonotonic.

This means that there may be a slight upturn in the sig-

nal level at the low end of the VGC control range (typi-

cally about 1dB). Because of the stability implications,

we suggest that the user not plan on attenuating past

35dB within a feedback loop.

Power Amplifier

The VGC stage passes the signal to the power amplifi-

er. This class AB stage will produce at least 20dBm of

output power for almost the complete transmit frequen-

cy range (with TA = +25°C). See Typical Operating

Characteristics.

BADJ Input

The BADJ input adjusts the bias of the output stage.

Increasing this voltage decreases bias current in the

output devices, which increases efficiency, but also

increases harmonic distortion (since the stage will be

pushed further toward class B operation). Decreasing

BADJ’s voltage increases bias current in the output

devices, resulting in higher output power and less har-

monic distortion. Be sure to optimize BADJ for your

application.

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