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TDK5111

ASK/FSK Transmitter 315 MHz

Infineon Technologies 

TDK 5111

Functional Description

3.4.3 Power Amplifier

For operation at 315 MHz, the power amplifier is fed with the VCO frequency

divided by 2. It is possible to feed the power amplifier directly from the voltage

controlled oscillator. This is controlled by FSEL (pin 15) as described in the

table below. This is not recommended for this frequency range.

Table 3-5

FSEL (pin 15)

Low1)

Open2)

1) Low: Voltage at pin < 0.5 V

2) Open: Pin open

Radiated Frequency Band

315 MHz

630 MHz (not recommended)

The Power Amplifier can be switched on and off

by the signal at ASKDTA (pin 6).

Table 3-6

ASKDTA (pin 6)

Low1)

Open2), High3)

1) Low: Voltage at pin < 0.5 V

2) Open: Pin open

3) High: Voltage at pin > 1.5 V

Power Amplifier

OFF

ON

The Power Amplifier has an Open Collector output at PAOUT (pin 14) and

requires an external pull-up coil to provide bias. The coil is part of the tuning and

matching LC circuitry to get best performance with the external loop antenna.

To achieve the best power amplifier efficiency, the high frequency voltage swing

at PAOUT (pin 14) should be twice the supply voltage.

The power amplifier has its own ground pin PAGND (pin 13) in order to reduce

the amount of coupling to the other circuits.

In all 315 MHz applications, the pin FSEL is connected to ground.

3.4.4 Low Power Detect

The supply voltage is sensed by a low power detector. When the supply voltage

drops below 2.15 V, the output LPD (pin 2) switches to the low-state. To mini-

mize the external component count, an internal pull-up current of 40 µA gives

the output a high-state at supply voltages above 2.15 V.

The output LPD (pin 2) can either be connected to ASKDTA (pin 6) to switch off

the PA as soon as the supply voltage drops below 2.15 V or it can be used to

inform a micro-controller to stop the transmission after the current data packet.

Wireless Components

3-9

Specification, October 2002

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