AT86RF211DAI-R datasheet(20/48 Pages) ATMEL

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AT86RF211

1942C–WIRE–06/02

Power Amplification

The Power Amplifier has been built to deliver more than +10 dBm, i.e. 10 mW in the

three popular frequency bands. This power level is intended to be measured on the

aerial port with a correct output matching network. Note that a correct calculation of the

matching network guarantees an optimal power efficiency.

Naturally, the greater the PA output voltage swing, the better the power efficiency. As

the PA output is supplied through an inductor, a swing of 2 x V

DD is possible. In practice,

due to saturation effects, the voltage swing is limited to approximately (2 x V

DD)-1V.

With a power supply voltage of 3V, the PA output voltage is 5V peak-to-peak, or

1.77 V

EFF.

Figure 24. Output of the Power Amplifier

The PA must be correctly matched to deliver the best efficiency in terms of output power

and current consumption. Here is an example of the typical recommended output net-

work in the 868 MHz band:

Figure 25. Output Matching at 868 MHz

Note:

The filter is designed to meet relevant regulations. Please refer to application note for details.

A benefit of this network is to filter the output signal harmonic levels; hence it can be

designed to meet a particular regulation.

It is mandatory to implement low impedance grounding techniques. Excessive inductor

values to ground will not only limit the PA output voltage swing, but may also trigger RF

instability. Board design is vital to avoid parasitic loss when high output power is needed

(direct short connection to a single low impedance ground plane).

PA output

1.5 nH

12 nH

Vcc

Power supply

filtering

Supply

inductor

Ω

aerial

~ 50

Ω matched filtering

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