Micrel, Inc.

MICRF300

April 2012

7

M9999-041712-B

Functional Description

Output Bias and Matching

The MICRF300 is a low-noise amplifier (LNA) which

operates over the 100 to 1000MHz frequency range. The

device operates from a 1.8V to 3.6V voltage supply, where

it consumes 2.5mA of supply current during operation, and

1

μA (max) of current in shutdown. A simple LC input

matching network is required to optimize the device for

best noise figure. A simple LC network is required to bias

the output stage and match the output to the following

stage.

Recommended matching networks have been

provided for 315MHz, 433.92MHz and 900MHz. See

Evaluation Board and Bill of Materials

for recommended

component values. See Figure 1 for Block Diagram of the

MICRF300.

The output stage has an internal pull-up resistor of 250

Ω.

To resonate out any parasitic capacitance and to increase

output swing capability, a multi-layer ceramic inductor

should be connected from the RF output, RFOUT (Pin 5)

Typical Performance and Matching Component Values

table of the data sheet.

Enable

The MICRF300 features a logic-level enable, EN (Pin 1). A

logic-level low disables the device. A logic-level High

enables the device. The value of the input DC-blocking

capacitor will affect the enable and disable time of the

device.

Input Matching

The RF input pin, RFIN (Pin 3) is directly connected to the

base of the RF input device. In normal operation, the DC

voltage of this pin is one diode above GND.

The

MICRF300 requires an input matching network for optimal

noise figure, gain and linearity. A series inductor and a DC-

blocking capacitor are required to implement this network.

A high-Q, wire-wound type inductor is recommended for

lowest noise figure at 315MHz and 433.92MHz.

A

standard multi-layer ceramic inductor can be used, but the

noise figure degrades by 0.2 dB. At 900MHz, a standard

multi-layer ceramic inductor may be used as the

inductance value is very low, and the Q does not make a

measurable difference. See recommended component

values in the Typical Performace and Matching Component

Values

section of the data sheet.

Power Supply Bypassing

Minimum supply bypassing is needed on PCB board to

filter out AC fluctuations in supply voltage. It is achieved by

placing a 0.1

μF capacitor as close as possible between the

MICRF300 Evaluation Board for recommend layout.

Functional Diagram

Figure 1: Block Diagram