LNA linearity is required for cross-modulation suppres-

sion. Use HGLL mode when the transmitter is off and

cross-modulation is not a concern. The LNAs are

designed to minimize input VSWR when changing

modes. Use low-gain mode for receiving large signals

and when high sensitivity is not required. The cellular

band provides an additional gain mode (MG) for

improved IP3 margin in CDMA medium-level interfer-

ence condition.

Downconverters

The downconverters in these devices are double-

balanced mixers. The cellular and PCS mixers have

three gain modes: high linearity, low linearity, and low

gain. The cellular and PCS mixers can route the IF sig-

nal to either IF0 or IF1 port. IF_SEL = low routes the IF

signal to IF0 port; IF_SEL = high routes the IF signal to

IF1 port. The GPS mixer has only one mode, and it has

a dedicated IF port (Table 2). All mixer inputs include

on-chip matching networks to reduce the external com-

ponent count.

LO Generation

Table 3 shows the options for the LO generation. The

on-chip LO divider or multiplier allows triple-band oper-

ation with a single VCO. The MAX2351 and MAX2531

have an LO multiplier that doubles the cellular band

VCO for PCS band operation. Conversely, the

MAX2358, MAX2537, and MAX2538 include an LO

divider that divides the PCS VCO frequency down to

cellular frequency band. The GPS LO is generated by a

fractional frequency scaler, which enables a single

VCO for operation in all three bands. The MAX2530 is

designed for operation with a dual-band VCO.

The PLL buffer output is provided for phase-locked

loop operation. The PLL pin serves two functions: RF

output signal for phase-locked loop operation and logic

input to enable or disable this buffer. A logic high

applied to this pin enables the PLL buffer; a logic low

disables the buffer.

A buffered LO output is provided to drive a transmit

upconverter. It is controlled by the BUFFEN input. For

time-division duplex applications, the buffer is available

to drive the transmitter even when the rest of the chip is

shut down. The port is internally AC-coupled, so a DC-

blocking capacitor is not required.

Bias Control

The bias control input (BIAS pin) controls the IC bias

current. Typically, connect a 20k

Ω resistor to ground for

normal operation. Smaller bias resistor values increase

the supply current and linearity.

Applications Information

Cascaded LNA/Mixer Performance

The LNA and mixer design optimizes cascaded perfor-

mance in all gain and linearity modes. In high-gain/high-

linearity mode, both the LNA and mixer have low noise

figure, high gain, and high linearity. In this mode, the

LNA has extra-high linearity for superior cross-modula-

tion suppression. The high-gain/low-linearity mode is

used when the transmitter is off and cross-modulation is

not a concern. In the ultra-low-gain mode, the received

signal is strong enough that sensitivity is not the limiting

factor. This mode focuses on minimizing supply current.

Tables 4, 5, 6 summarize the cascaded performance.

LNAs

The LNA inputs require external matching networks to

optimize gain, linearity, noise figure, and return loss. A

simple LC match is sufficient as shown in the Typical

Application Circuit. The cellular and GPS LNA outputs

are internally matched. The PCS LNA output requires

external matching elements. Table 7, 8, 9 show the S-

parameters for each LNA. Tables 13, 14, 15 show LNA

noise parameters.

Mixers

All mixer inputs are internally matched. The GPS and

PCS mixer inputs require a DC-blocking capacitor; the

cellular mixer does not. All IF outputs must be induc-

used as part of the matching network. Because the dif-

ferential IF output port is high impedance, a load resis-

tor is typically used to ease the matching and establish

the gain. A 3.3k

Ω resistor is recommended for IF0 and

IF1, and 8.2k

Ω for the GIF port. The equivalent parallel

RC impedance of the IF ports is typically 12.2k

Ω in par-

allel with 0.75pF. Tables 10, 11, 12 show S-parameters

for the mixer input points.

Quadruple-Mode PCS/Cellular/GPS LNA/Mixers

10

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ABBREVIATION

MODE

HGHL

High gain/high linearity

HGLL

High gain/low linearity

MG

Midgain

LG

Low gain

ULG

Ultra-low gain

HL

High linearity

LL

Low linearity

Table 1. Abbreviation for LNA and Mixer

Modes