Envelope tracking amplifier for a transmitter having a voltage mapping linearly related to the square of the amplitude of the baseband signal

1. A method of transmitting an RF signal derived from baseband samples, comprising:

modulating information derived from the baseband samples onto a RF carrier, and amplifying the modulated signal in an amplifier,

wherein the amplifying comprises applying a voltage mapping, provided to the amplifier, to an amplitude of the baseband samples to control the amplifier supply, wherein the voltage mapping provided to the amplifier is a linear function of a square of the amplitude of the baseband samples,

determining a power mapping signal representative of a mapping giving optimal amplifier power efficiency,

forming the voltage mapping to be tangential to the power mapping signal, and

selecting a point on the power mapping signal at which the voltage mapping signal is tangential to the power mapping signal,

wherein the point is a point corresponding to a square of the average signal amplitude or the point is in a range between 0.75 times a square of the average signal amplitude and 3 times the square of the average signal amplitude.

2. The method according to claim 1 , wherein the baseband samples comprise in phase and quadrature samples.

3. The method according to claim 1 , further comprising selecting the point based upon out-of-band noise.

4. The method according to claim 1 wherein the RF signal is a signal meeting LTE standards.

5. A transceiver comprising:

a receiver for receiving signals from a receive antenna; and

a transmitter configured to transmit, via a transmit antenna, an RF signal derived from baseband samples, the transmitter comprising:

a modulator for modulating information derived from the baseband samples onto a RF carrier;

an amplifier for amplifying the modulated signal for application to the transmit antenna;

processing circuitry for deriving an amplitude signal indicative of an instantaneous amplitude of a square of the baseband samples, the processing circuitry configured to apply a voltage mapping, provided to the amplifier, to the amplitude signal to provide a resultant signal; and

an envelope modulator for using the resultant signal to control the voltage applied to the amplifier, wherein the voltage mapping provided to the amplifier is a linear function of the square of the amplitude of the baseband samples;

wherein the processing circuitry is further configured to determine a power mapping signal representative of a mapping giving optimal amplifier power efficiency, form the voltage mapping to be tangential to the power mapping signal, and select a point on the power mapping signal at which the voltage mapping signal is tangential to the power mapping signal,

wherein the point is a point corresponding to a square of the average signal amplitude or the point is in a range between 0.75 times a square of the average signal amplitude and 3 times the square of the average signal amplitude.

6. The transceiver according to claim 5 wherein the baseband samples are in-phase and quadrature signals.

7. The transceiver according to claim 5 wherein the baseband samples are digital.

8. The transceiver according to claim 5 wherein the transmit and receive antennas are a single duplex antenna.

9. An FDD transceiver adapted for LTE signals, comprising the transceiver of claim 5 .

10. A transceiver comprising:

a receiver for receiving signals from a receive antenna; and

a transmitter configured to transmit, via a transmit antenna, an RF signal derived from baseband samples, the transmitter comprising:

a modulator for modulating information derived from the baseband samples onto a RF carrier;

an amplifier for amplifying the modulated signal for application to the transmit antenna;

processing circuitry for deriving an amplitude signal indicative of an instantaneous amplitude of a square of the baseband samples, the processing circuitry configured to apply a voltage mapping, provided to the amplifier, to the amplitude signal to provide a resultant signal; and

an envelope modulator for using the resultant signal to control the voltage applied to the amplifier, wherein the voltage mapping provided to the amplifier is a linear function of the square of the amplitude of the baseband samples;

wherein the processing circuitry is further configured to determine a power mapping signal representative of a mapping giving optimal amplifier power efficiency, form the voltage mapping to be tangential to the power mapping signal, and select a point on the power mapping signal at which the voltage mapping signal is tangential to the power mapping signal and based upon out-of-band noise.

11. A method of transmitting an RF signal derived from baseband samples, comprising:

modulating information derived from the baseband samples onto a RF carrier, and amplifying the modulated signal in an amplifier,

wherein the amplifying comprises applying a voltage mapping, provided to the amplifier, to an amplitude of the baseband samples to control the amplifier supply, wherein the voltage mapping provided to the amplifier is a linear function of a square of the amplitude of the baseband samples,

determining a power mapping signal representative of a mapping giving optimal amplifier power efficiency,

forming the voltage mapping to be tangential to the power mapping signal, and

selecting a point on the power mapping signal at which the voltage mapping signal is tangential to the power mapping signal and based upon out-of-band noise.