Amplifier composite triple beat (CTB) reduction by phase filtering
View Patent ↗In a broadband communication system there are multi-stage power amplifier systems for amplifying the power of radio-frequency (RF) communication signals. Each stage of the amplifier system results in composite triple beat (CTB) distortion, and if the phase of the CTB distortions are approximately the same (i.e. are in-phase), then the amplitudes of the distortions are added (i.e. “20 dB” rule). The amplifier system of the invention includes one or more phase filters positioned in series between the power amplifier stages. The phase filters are adapted to shift the phase of the communication signals, so that the phase of CTB distortions, resulting from the amplification of the communication signals in the amplifier stages between the phase filters, are substantially different (i.e. are out-of-phase). Thus, only the power of the CTB distortions are added (i.e. “10 dB” rule).
1. An amplifier, comprising:
a first amplifier configured to receive a wideband input signal having a carrier signal and output a first amplified signal, the first amplifier introducing first CTB distortions of the carrier signal into the first amplified signal;
a first phase filter coupled to said first amplifier so as to receive said first amplified signal as an input, said first phase filter configured to output a first phase shifted signal;
a second amplifier coupled to said first phase filter so as to receive said first phase shifted signal and to output a second amplified signal, the second amplifier introducing second CTB distortions of the carrier signal; and
the first phase filter configured to shift a phase of the first amplified signal to an extent that substantially reduces accumulation of amplitudes of the CTB distortions produced by the first and second amplifiers while causing power of the CTB distortions produced by the first and second amplifiers to substantially accumulate.
2. The amplifier of claim 1 , further comprising:
a second phase filter coupled to said second amplifier so as to receive said second amplified signal as an input, said second phase filter configured to output a second phase shifted signal;
a third amplifier coupled to said second phase filter so as to receive said second phase shifted signal and to output a third amplified signal, the third amplifier introducing third CTB distortions; and
the first phase filter configured to shift a phase of the first amplified signal to an extent that substantially reduces accumulation of amplitudes of CTB distortions produced by the first, second, and third amplifiers while causing power of the CTB distortions produced by the first, second, and third amplifiers to substantially accumulate.
3. The amplifier of claim 2 , further comprising:
the first and second phase filters configured to shift a phase of the first amplified signal and the second amplified signal, respectively, to extents that substantially reduce accumulation of amplitudes of CTB distortions produced by the first, second, and third amplifiers while causing power of the CTB distortions produced by the first, second, and third amplifiers to substantially accumulate.
4. The amplifier of claim 1 , further comprising:
the phase shift of the first amplified signal between 15 and 60 degrees, and the phase shift of the second amplified signal between 15 and 60 degrees.