Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Reexamination Certificate
2001-12-14
2003-10-14
Choe, Henry (Department: 2817)
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
C330S136000, C455S126000
Reexamination Certificate
active
06633199
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an amplifier circuit for delivering a signal which varies in amplitude as well as in phase or frequency, preferably a radio frequency amplifier circuit.
The invention relates as well to a radio transmitter or a cellular telephone comprising an amplifier circuit in their aerial output stage.
Further, the invention relates to a method for controlling a radio frequency output amplifier circuit in a radio transmitter, and to the use of said method in a mobile radio transmitter.
From the article: Leonard R. Kahn: “Single-Sideband Transmission by Envelope Elimination and Restoration”, Proceedings of the I.R.E., 1952, pp. 803-806, a Single-Sideband (SSB) Transmitter is known, wherein the phase and amplitude components of an input signal are separated and amplified independently before being mixed in a final output stage.
It is a disadvantage in this transmitter that modulating the amplitude at a high power level tends to generate considerable amounts of spurious signals.
From the article: V. Petrovic & W. Gosling: “Polar-Loop Transmitter”, Electronics Letters, 10
th
May 1979 Vol. 15 No. 10, pp. 286-288, a Polar Modulation Feedback Linearisation System for an SSB Transmitter is known, wherein the modulated output from a Radio Frequency Power Amplifier (RF PA) is being controlled by means of two closed loops, each having the same modulated Intermediate Frequency (IF) Signal as the controlling variable. A first loop controls the Amplitude Modulation (AM) or the “envelope” of the RF output signal relative to the IF signal, and a second loop controls the Phase Modulation (PM) of the RF output signal relative to the IF signal. Polar representation of the RF signal vector is used in the article, the vector angle representing the signal phase and the vector magnitude representing the signal amplitude.
It is a disadvantage in systems of the two types mentioned, that the gain of known RF power amplifiers is varying with the power level. This entails poor linearity at high power levels and in the latter system a poor stability of the closed loop. These deficiencies often cause spurious signals or sidebands to be emitted.
The object of the invention is to provide an amplifier circuit for amplifying and delivering signals which are amplitude modulated as well as phase or frequency modulated, the amplifier having improved stability and linearity throughout the entire power level range.
It is a further object of the invention to provide an amplifier circuit of said type with an improved power efficiency.
In particular for transmitter power amplifier circuits used in cellular telephones (mobile phones), stability and linearity are of prime importance in order to utilise efficiently the very limited frequency bands available for this service. Also, a high power efficiency is very important in mobile equipment, in order to obtain a long operating time from a given battery capacity.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides an amplifier circuit for receiving one or more input signals and delivering an output signal which varies in amplitude and in phase and/or frequency, the circuit comprising a power amplifier producing said output signal, a first feedback circuit providing feedback of the amplitude value of said output signal, and wherein said feedback circuit has its gain controllable in dependency of one or more properties of the input signals, the output signal or both, characterised in that the circuit is arranged to differentiate between output power levels to achieve constant gain in the amplitude loop.
Preferably, the circuit is arranged to control the amount of signal feedback to the input of the amplifier according to the output power level.
Preferably, the circuit is arranged to increase the amount of signal feedback to the input of the amplifier at high output power levels, and decrease the amount of signal feedback at low output power levels.
Preferably, the circuit comprises a second feedback circuit providing feedback of the phase or frequency of said output signal, said feedback circuits constituting a closed feedback loop together with said power amplifier.
In one embodiment, the invention provides an amplifier circuit for receiving one or more input signals and delivering an output signal which varies in amplitude and in phase or frequency, the circuit comprising a power amplifier producing said output signal, a first feedback circuit providing feedback of the amplitude value of said output signal, and a second feedback circuit providing feedback of the phase or frequency of said output signal, said feedback circuits constituting closed feedback loops together with said power amplifier, the object mentioned is met in that at least one of said feedback circuits has its gain controllable in dependency of one or more properties of the input signals, the output signal, or both.
Hereby, the phase or frequency linearity as well as the amplitude linearity for the amplifier circuit are substantially improved. This improvement in linearity may advantageously be exploited to achieve better signal qualities such as lower levels of spurious signals, thus enabling e.g. a closer channel spacing or a higher modulation factor without inter-channel cross-talk.
In addition, said improvement may be exploited by the use of power amplifiers having higher power efficiencies, such power amplifiers most often having a marked non-linear behaviour. The use of power amplifiers with higher power efficiencies is generally favourable, but especially so in mobile equipment such as cellular telephones.
It is generally preferred that the output signal is an RF signal. Hereby, the advantages of the amplifier circuit are utilised efficiently in that the amplifier circuit enables a radio transmitter output signal of high quality to be produced, this signal meeting the demands for radio transmissions in to-day's very crowded radio frequency spectrum.
Preferably, the gain of one or more of said controllable gain feedback circuits is controlled by a gain control signal.
Hereby, said gain may be controlled from a sub-system such as e.g. a digital signal processor.
In a preferred embodiment, the first feedback circuit has its gain controllable in dependency of the amplitude of the output signal.
This will enable stabilisation of the amplitude feedback loop gain in the case where the gain of the power amplifier is varying with the output signal amplitude. This is most often the case in power amplifiers with a high power efficiency. In this situation, a substantially constant, high loop gain will be achievable without risk of the varying gain of the power amplifier leading to instabilities in the amplitude loop.
It is preferred that the second feedback circuit constitutes a phase lock loop together with said power amplifier.
This will enable a high phase linearity of the output power amplifier, which will tend to lower any phase distortion arising from imperfections in the power amplifier.
“Cross-talk” from the amplitude modulation to the phase or frequency modulation (or: phase or frequency distortion, respectively, generated by the amplitude modulation) in amplifiers processing compound modulated signals will always be present to some small extent, due to the fact that the shift of the amplifier gain introduced by the shift of the modulated amplitude will in itself affect the momentary phase or frequency, respectively, of the signal.
Substantially cross-talk from the amplitude modulation to the phase or frequency which will normally be encountered when using a power amplifier with a poor amplitude linearity for amplifying signals that are both amplitude and phase or frequency modulated, is however avoided in the embodiments of the invention with both an amplitude feedback loop and a phase locked loop, because the phase distortion generated from the amplitude modulated signal by the amplitude linearity defects of the power amplifier are cancelled by the phase linearity feedback of the phase locked loop.
This is so because the phase distortio
Fallesen Carsten
Nielsen Per Asbeck
Antonelli Terry Stout & Kraus LLP
Choe Henry
Nokia Corporation
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