MICRF114 datasheet(5/34 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

Preliminary

DS50002416A-page 5

MICRF114

1.8

Frequency Synthesizer

The frequency synthesizer is a fully integrated PLL with

a fixed feedback division ratio. It operates on a single

frequency that is determined by the reference crystal.

The VCO within the PLL operates directly at the

transmit frequency to save power. The VCO also has a

wide tuning range to cover most of the popular

frequencies below 500 MHz.

1.9

Transmit Path

The main element of the transmit path is the RF Power

Amplifier (PA). Since typical applications use monopole

antennas, the output is single-ended. It must be biased

to VDD using an inductor. This configuration enables

high-voltage swing, thereby reducing the required

supply current for the specified output power. The

output power is programmable by the MCU in 1 dB

steps. This enables the current consumption and

transmit range to be optimized according to the

product requirements of the customers. Additionally,

compliance with the relevant regulations can be

ensured with different antenna gains.

To ease design-in and keep the BOM as low as

possible, the output capacitance of the PA is

programmable by the MCU. As a result, the impedance

matching circuit between the RF output and the

antenna requires fewer elements and is easier to

optimize. A modulator circuit is used to control the

slope of the output power ramping on and off. This is to

prevent steep supply current transients which may

result in a spectrum splatter.

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