400MHz to 2.5GHz Upconverter Mixers

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_______________Detailed Description

The MAX2660/MAX2661/MAX2663/MAX2671/MAX2673

are 2.5GHz double-balanced upconverter mixers

designed to provide optimum linearity performance for

a specified supply current. These upconverter mixers

use single-ended RF, LO, and IF port connections,

except for the MAX2673, which uses a differential IF

port. An on-chip bias cell provides a low-power shut-

down feature. See the Selector Guide for device fea-

tures and comparison.

__________Applications Information

Local-Oscillator (LO) Input

The LO input is a single-ended broadband port with a

return loss of better than 8dB from 600MHz to 2.5GHz.

The LO signal is mixed with the input IF signal, and the

resulting upconverted output appears on the RFOUT

pin. AC-couple the LO pin with a capacitor having less

than 3

Ω reactance at the LO frequency. The

MAX2671/MAX2673 include an internal LO buffer and

require an LO signal ranging from -10dBm to +5dBm,

while the MAX2660/MAX2661/MAX2663 require an LO

signal ranging from -5dBm to +2dBm.

IF Input

The MAX2660/MAX2661/MAX2663/MAX2671 have a

single-ended IF input port, while the MAX2673 has a

differential IF input port for high-performance interface-

to-differential IF filters. AC-couple the IF pin(s) with a

capacitor. The typical IF input frequency range is

40MHz to 500MHz. For further information, see the IF

Port Impedance vs. IF Frequency graph in the Typical

Operating Characteristics.

RF Output

The RF output frequency range extends from 400MHz

to 2.5GHz. RFOUT is a high-impedance, open-collector

proper biasing. For optimum performance, implement

an impedance-matching network. The configuration

and values for the matching network depend on the fre-

quency, performance, and desired output impedance.

For assistance in choosing components for optimal per-

formance, see Table 1 as well as the RF Output

Impedance vs. RF Frequency graph in the Typical

Operating Characteristics.

Power Supply and

S

SH

HD

DN

N Bypassing

Proper attention to supply bypassing is essential for a

capacitor in parallel with an RF capacitor (Table 2). Use

separate vias to the ground plane for each of the

bypass capacitors and minimize trace length to reduce

inductance. Use separate vias to the ground plane for

each ground pin. Use low-inductance ground connec-

tions.

Decouple SHDN with a 100pF capacitor to ground to

minimize noise on the internal bias cell. Use a series

resistor (typically 100

Ω) to reduce coupling of high-fre-

quency signals into the SHDN pin.

______________________Layout Issues

A well-designed PC board is an essential part of an RF

circuit. For best performance, pay attention to power-

supply issues as well as to the layout of the RFOUT

matching network.

Power-Supply Layout

To minimize coupling between different sections of the

IC, the ideal power-supply layout is a star configuration

board. At the end of each trace is a bypass capacitor

that has low ESR at the RF frequency of operation. This

pin. At high frequencies, any signal leaking out of one

supply pin sees a relatively high impedance (formed by

an even higher impedance to any other supply pin, as

well as a low impedance to ground through the bypass

capacitor.

Impedance-Matching Network Layout

The RFOUT matching network is very sensitive to lay-

out-related parasitics. To minimize parasitic induc-

tance, keep all traces short and place components as

close as possible to the chip. To minimize parasitic

capacitance, use cutouts in the ground plane (and any

other plane) below the matching network components.