High efficiency output stage amplification for radio frequency (RF) transmitters
View Patent ↗Highly power efficient transmitter output stage designs are provided. In an embodiment, the probability density function (PDF) of an input signal is divided into a plurality of regions, and samples of the input signal are processed depending on the region of the PDF within which they fall. The PDF can be divided between an inner region corresponding to samples of the input signal that are within a predetermined amplitude range, and outer regions corresponding to samples of the input signal that are outside of the predetermined amplitude range. Samples of the input signal that fall in the inner region are processed by a class A biased amplifier and samples of the input signal that fall in the outer regions are processed by a class B biased amplifier. Output stage designs according to embodiments can be implemented as power amplifiers or power digital-to-analog converters (DACs).
1. A power digital-to-analog converter (DAC), comprising:
an amplitude mapper configured to receive an input signal and to generate a first input constituent signal and a second input constituent signal from the input signal;
a first DAC configured to receive the first input constituent signal and to generate a first current signal;
a second DAC configured to receive the second input constituent signal and to generate a second current signal; and
a combiner configured to combine the first and second current signals to generate an output signal of the power DAC,
wherein the first DAC is biased with a first supply voltage, and
wherein the second DAC is biased with a second supply voltage higher than the first supply voltage when the second input constituent signal is non-zero, and is biased with a third supply voltage lower than the first supply voltage when the second input constituent signal is zero.
2. The power DAC of claim 1 , wherein each of the first and second input constituent signals corresponds to a respective portion of the input signal, and wherein a sum of the first and second input constituent signals is equal to the input signal.
3. The power DAC of claim 1 , wherein the first input constituent signal corresponds to samples of the input signal that are within a predetermined amplitude range, and wherein the second input constituent signal corresponds to samples of the input signal that are outside the predetermined amplitude range.
4. The power DAC of claim 1 , further comprising:
a current steering stage configured to selectively couple the first and second current signals to the combiner.
5. The power DAC of claim 4 , wherein the combiner comprises:
a first winding biased with the first supply voltage;
a second winding biased with the second supply voltage;
an output winding, coupled to a load, configured to generate the output signal of the power DAC.
6. The power DAC of claim 5 , wherein the current steering stage comprises:
a first current steering cell configured to couple the first current signal of the first DAC to the first winding when the input signal is within a predetermined amplitude range and to the second winding when the input signal is outside the predetermined amplitude range; and
a second current steering cell configured to couple the second current signal of the second DAC to a dump supply voltage when the input signal is within the predetermined amplitude range and to the second winding when the input signal is outside the predetermined amplitude range.
7. The power DAC of claim 6 , wherein the dump supply voltage corresponds to the third supply voltage.
8. The power DAC of claim 4 , wherein the power DAC is implemented in a multi-chip module (MCM).
9. The power DAC of claim 8 , wherein the MCM comprises:
a first chip comprising the first and second DACs, implemented using a first process; and
a second chip comprising the current steering stage, implemented using a second process.
10. A power digital-to-analog converter (DAC), comprising:
an amplitude mapper configured to receive an input signal and to generate a first input constituent signal that corresponds to samples of the input signal that are within a predetermined amplitude range, and a second input constituent signal that corresponds to samples of the input signal that are outside the predetermined amplitude range;
a first DAC configured to receive the first input constituent signal and to generate a first current signal;
a second DAC configured to receive the second input constituent signal and to generate a second current signal; and
a current steering stage configured to couple the first current signal to a first supply voltage when the input signal is within the predetermined amplitude range and to couple the second current signal to a second supply voltage higher than the first supply voltage when the input signal is outside the predetermined amplitude range.
11. The power DAC of claim 10 , wherein the current steering stage is further configured to couple the first current signal to the second supply voltage when the input signal is outside the predetermined amplitude range, and to couple the second current signal to a dump supply voltage lower than the first supply voltage when the input signal is within the predetermined amplitude range.
12. The power DAC of claim 11 , wherein the current steering stage comprises a class A current steering cell configured to selectively couple the first current signal to the first supply voltage or the second supply voltage, and a class B current steering cell configured to selectively couple the second current signal to the second supply voltage or the dump supply voltage.
13. The power DAC of claim 10 , wherein the first DAC is biased with the first supply voltage, and wherein the second DAC is biased with the second supply voltage when the input signal is outside the predetermined amplitude range.
14. The power DAC of claim 10 , wherein a sum of the first input constituent signal and the second input constituent signal is equal to the input signal.
15. A power amplifier, comprising:
an input stage configured to receive an input signal and to generate first and second current signals; and
a current steering stage configured to selectively couple the first and second current signals to a first supply voltage when the input signal is within a predetermined amplitude range and to a second supply voltage higher than the first supply voltage when the input signal is outside the predetermined amplitude range.
16. The power amplifier of claim 15 , further comprising:
a combiner configured to combine the first and second current signals to produce an output current signal in a load.
17. The power amplifier of claim 16 , wherein the combiner comprises:
a first winding having a center tap biased with the first supply voltage;
a second winding having a center tap biased with the second supply voltage; and
an output winding, coupled to the load, configured to generate the output current signal.
18. The power amplifier of claim 17 , wherein the current steering stage is configured to couple the first and second currents to the first winding when the input signal is within the predetermined amplitude range and to the second winding when the input signal is outside the predetermined amplitude range.
19. The power amplifier of claim 15 , wherein the input stage includes a digital-to-analog converter (DAC).
20. The power amplifier of claim 15 , wherein the input stage comprises:
an amplitude mapper configured to receive the input signal and to generate a first input constituent signal and a second input constituent signal from the input signal;
a first DAC configured to receive the first input constituent signal and to generate the first current signal; and
a second DAC configured to receive the second input constituent signal and to generate the second current signal.