Enhanced efficiency LDMOS based feed forward amplifier
View Patent ↗A feed forward amplifier employing high efficiency main and/or error amplifiers with amplifier devices biased in a lower bias class. Small signal nonlinearities in the gain response of the amplifier devices are compensated by a small signal gain adjustment circuit. The resulting gain response is substantially linear over the entire usable range of RF input power.
1. An amplifier, comprising:
an input for receiving a signal to be amplified;
an amplifier device biased to have a nonlinear gain characteristic in the small signal region;
a small signal linearization circuit coupled between said input and said amplifier device for compensating for the small signal nonlinearity of said amplifier device, said small signal linearization circuit comprising an envelope detector an a gain control circuit controlled in response to the envelope of the input signal detected by the envelope detector; and
an output coupled to the amplifier device for outputting the amplified signal.
2. An amplifier as set out in claim 1 , wherein said amplifier device is an LDMOS transistor.
3. An amplifier as set out in claim 1 , wherein said amplifier device is biased in lower class AB or in class B.
4. An amplifier as set out in claim 1 , wherein said small signal linearization circuit reduces the input signal magnitude over a portion of the gain response of the amplifier device corresponding to the small signal region.
5. An amplifier as set out in claim 4 , wherein said small signal linearization circuit has a gain response substantially opposite to said gain response of the amplifier device.
6. An amplifier as set out in claim 4 , wherein the portion of the gain response of the amplifier device corresponding to said small signal region comprises the range of about −15 dB to −5 dB of maximum input power.
7. An amplifier, comprising:
an input for receiving a signal to be amplified;
an amplifier device biased to have a nonlinear gain characteristic in the small signal region;
a small signal linearization circuit coupled between said input and said amplifier device for compensating for the small signal nonlinearity of said amplifier device, said small signal linearization circuit comprising a first and second diode in parallel coupled between the signal input path and ground and a resistor coupled in series with the first and second diode and ground; and
an output coupled to the amplifier device for outputting the amplified signal.
8. An amplifier as set out in claim 1 , wherein said small signal linearization circuit further comprises a video amplifier coupled between said envelope detector and said gain control circuit.