315MHz/433MHz Low-Noise

Amplifier for Automotive RKE

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5

Detailed Description

The MAX2634 LNA with low-power shutdown mode is

optimized for 308MHz, 315MHz, 418MHz, and 433MHz

automotive RKE applications, which are required to

operate over the -40°C to +125°C automotive tempera-

ture range. The device reduces component count by

integrating the output matching and DC-blocking com-

ponents, and only requires a single inductor to match

the input for best noise figure and input return loss. An

integrated logic-controlled low-power shutdown mode

reduces power consumption to 0.1µA and replaces the

two transistors typically required to implement the shut-

down function in discrete-based RKE LNA solutions.

Input Matching

The MAX2634 requires an off-chip input matching net-

work. The

Functional Diagram/Typical Operating Circuit

shows the recommended input-matching network com-

ponent values for operation at 315MHz and 433MHz.

These values are optimized for the best simultaneous

gain, noise figure, and return loss performance. Table 1

lists typical input and output impedances.

Pin Description

PIN

NAME

FUNCTION

1, 3

GND

Ground. Use minimum path to ground plane to minimize inductance.

2

SHDN

Shutdown Input. A logic-level high enables the LNA, and a logic-level low disables the LNA.

4

RFIN

RF Input. Requires an inductor to match the input for best noise figure and return loss. A DC-blocking

capacitor is required if the RFIN input will see a DC voltage or ground. See the Functional

Diagram/Typical Operating Circuit.

5

Supply Voltage. Bypass to ground with a 0.01µF capacitor as close as possible to the pin.

6

RFOUT

RF Output. Internally matched to 50

and incorporates an internal DC-blocking capacitor.

INPUT IMPEDANCE

OUTPUT IMPEDANCE

FREQUENCY (MHz)

RX

R

X

100

58

-438

92

-94

200

43

-216

92.1

-50

308

29

-139

91.2

-35.8

315

29.4

-137

91

-35

418

29.2

-101

90.5

-30

434

28.5

-96

89.5

-29.3

500

26.4

-83

91

-28.2

600

26.7

-69

87.5

-27.3

Table 1. Typical Input and Output Impedances in R+jX Format