Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
  • H03F1/32—Modifications of amplifiers to reduce non-linear distortion
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
  • H03F1/32—Modifications of amplifiers to reduce non-linear distortion
  • H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
  • H03F1/3247—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits using feedback acting on predistortion circuits

Definitions

• the present invention relates to a signal processing element, and in particular to an amplifying device which is linearised by suppression of intermodulation products in an output signal of the amplifying device.
• an output signal of an amplifying device does not present a perfect magnified reproduction of an input waveform due to a non-linear transfer characteristic.
• Such defects in an amplifying device are generally known as non-linear distortion and can be considered as an error in the output of an amplifier.
• Amplitude, harmonic and intermodulation distortion are examples and results of non-linear distortion.
• linearisation schemes include synthesis techniques (for example, LINC, CALLU or EER) , pre-and post-distortion methods, direct RF (radio frequency) feedback, envelope feedback technique, second harmonic injection and feedforward method.
• synthesis techniques function by decomposing an input signal of varying-envelope type to form two or more signals.
• LINC Linear amplification with Non-linear Components
• CALLUM Combined Analogue Locked Loop Universal Modulator
• EER envelope Elimination and Restoration
• the input signal is decomposed to form one constant-envelope signal for amplification and one varying-envelope control signal which does not require amplification.
• the last step in each of the synthesis techniques is the re-combination of the signals to form a high-power varying-envelope signal.
• the present invention seeks to provide an amplifying device in which non-linear distortion and connected problems associated with prior art devices, are at least alleviated.
• a circuit comprising a signal processing element for receiving an input signal, the signal processing element generating a first output signal at an output thereof, and a second output signal at an input thereof, wherein the second output signal is used to form an error signal to correct the first output signal .
• a method for processing a signal comprising the steps of receiving an input signal at an input of a signal processing element, generating a first output signal at an output of the signal processing element and a second output signal at an input of the signal processing element, and forming an error signal from the second output signal with which to correct the first output signal .
• the signal processing element can be any analogue signal processing element, and more specifically any non-linear electrical device. Generally, the signal processing element operates at radio frequency.
• the signal processing element can be, for example, a mixer, a gain/phase controller or an amplifier.
• an amplifier circuit comprising a main amplifier for receiving an input signal, the main amplifier generating a first output signal at an output thereof, and a second output signal at an input thereof, wherein the second output signal is used to form an error signal to correct the first output signal .
• a method for amplifying a signal comprising the steps of receiving an input signal at an input of a main amplifier, generating a first output signal at an output of the main amplifier and a second output signal at an input of the main amplifier., and forming an error signal from the second output signal with which to correct the first output signal .
• the error signal may be applied to the main amplifier output, or may be used to pre-distort the amplifier input.
• Figure 1 is schematic diagram of an amplifying device in accordance with an embodiment of the invention
• Figure 2 is a schematic diagram of an amplifying device in accordance with a second embodiment of the invention.
• Figure 3 is a schematic diagram of an amplifying device in accordance with a third embodiment of the invention.
• an input signal 2 is supplied to a coupler 4, which passes it into a main signal path 6 whilst isolating it from an error signal path 8.
• the signal in the main signal path 6 is supplied to an input port of a main amplifier 10.
• the signal from the output port of main amplifier 10 is then passed to an output coupler 16 via a fixed delay line 12 and a variable delay line 14.
• the main amplifier 10 generates a distortion signal within the device and therefore, even under perfect port matching conditions, some distortion signal is observed in the amplifier output signal leaving the output port and in an amplifier return signal leaving the input port of the main amplifier 10.
• the magnitude ratio of distortion spurious present at the output port of the main amplifier to distortion spurious present at the input port of the main amplifier is defined as the Device Distortion Ratio (DDR) . More specifically, if the main amplifier output signal contains a particular distortion spurious at a power of X dB , then the main amplifier return signal will contain a linearly related distortion spurious at a power of (X-DDR) dBW, if the DDR is expressed in dB.
• the main amplifier return signal is passed to the input port of an error amplifier 18 via the coupler 4.
• the main amplifier return signal In order for the main amplifier return signal to function as an error signal it must comprise a greater ratio of distortion signal to desired signal than is present in the main amplifier output signal. This condition is satisfied if the main amplifier 10 offers a good match to its source and load.
• the error signal is amplified by amplifier 18 and the resulting signal is then magnitude-phase conditioned by a fixed attenuator 20 and a variable attenuator 22.
• the error signal is then supplied to an input port of an amplifier 24.
• the resulting error signal is then passed to the output coupler 16, where it is compared to the main signal to give a linearised system output.
• the amplification required in the error signal path 8 is a function of the main amplifier gain, the main amplifier DDR, passive losses in the network, and the type .of couplers used. Therefore, the order and number of amplification and control components utilised in the error signal path can be varied provided the overall amplification in the error signal path remains at the required level .
• variable delay element 14 can be positioned in either the main signal path 6 or the error signal path 8.
• variable attenuation element 22 should be located in the error signal path 8 rather than the main signal path 6, to minimise power loss to the main signal after amplification by the main amplifier 10.
• variable delay element 14 in the configuration shown in Figure 1 may be replaced or supplemented by a phase control element without any detrimental effect on device functionality.
• a particular advantage of the invention is that the near-band instantaneous dynamic range of an amplifying device is increased. Also, due to the error 5 signal path 8 and the main signal path 6 being coupled together after the main amplifier 10, the amplifying device can operate in broadband with the associated advantages .
• the dynamic range of the error signal may be increased by further suppressing the residual wanted signal in the error path by controlled addition of the input signal 2 into the error signal path 8, either via the coupler 4 or by a separate path possibly containing
• Figure 1 shows an architecture in which an error signal is used to cancel the distortion in the amplifier output. It is also possible to use the error 0 signal to pre-distort the amplifier input.
• Figure 2 shows an input signal 26, which is supplied to a first coupler 28 and then passed to a second coupler 32, via a main signal path 30.
• the 5 first coupler 28 isolates the input signal 26 from an amplifier 40.
• the signal output from the second coupler 32 is passed to an input port of a main amplifier 42.
• the main amplifier 42 generates a distortion signal within the device and, as described in respect of Figure 1, some distortion signal is observed in an amplifier return signal leaving the input port of the main amplifier 42. A substantial part of this distortion signal is passed to a signal path 34 including a magnitude controller 36 and variable delay element 38.
• the signal path 34 may be considered to be an error signal path when certain conditions are fulfilled. Namely, the second coupler 32 must offer good isolation and the main amplifier 42 must be well matched at its input, with the result that the signal in path 34 contains a greater ratio of distortion signal to desired signal than at an output of the main amplifier 42.
• the error signal is passed to an input of the first coupler 28 via an amplifier 40.
• the error signal is injected into the main signal path 30 and is passed to the main amplifier 42 via the second coupler 32.
• the amplifier 40 functions to provide sufficient gain to overcome passive system losses and coupling losses, and to bring the error signal to an appropriate level for cancellation of the distortion within the main amplifier 42.
• the coupler 28 can be used to sample the signal in the main signal path 30, while the coupler 32 is then used to reinject the error signal into the signal which is being supplied to the amplifier 42.
• Figure 3 shows a third embodiment of the amplifying device of the present invention.
• An input signal 44 is incident to an input port of a coupler 46, and then passed to an input of a main amplifier 58 via main signal path 56.
• the main amplifier 58 generates a distortion signal within the device and, as described in respect of Figure 1, an amplifier return signal includes some distortion signal .
• the amplifier return signal passes to a magnitude controller 50 and a variable delay element 52 via the coupler 46. Again, where the coupler 46 offers efficient isolation and the main amplifier 58 is well matched at its input, then the signal in the error signal path 48 may be considered to be an error signal .
• the error signal is then passed to a negative resistance device 54 which functions to amplify the signal and return it along the error signal path 48.
• the negative resistance device 54 can be realised, for example, by an Impatt diode or Gunn diode.
• the same polar operation occurs on the error signal as it returns along the error signal path 48, resulting in a doubling of system sensitivity to variable delay element 52 and magnitude controller 50.
• the error signal is injected into the main signal path 56 (via coupler 46) and is passed to the input of the main amplifier 58. The error signal efficiently cancels the distortion within the main amplifier 58.
• the inventive concept of the present invention can be applied to the linearisation of analogue signal processing elements other than amplifiers, for example gain/phase controllers or mixers.
• the error signal can be isolated from either the input port or the local oscillator port.
• the present invention provides an amplifying device which has significant advantages over the conventional devices.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Amplifiers (AREA)
• Transmitters (AREA)

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• 2001
  • 2001-12-06 GB GB0129309A patent/GB2382936A/en not_active Withdrawn
• 2002
  • 2002-12-05 WO PCT/GB2002/005509 patent/WO2003049278A2/en not_active Ceased
  • 2002-12-05 EP EP02804314A patent/EP1508197A2/de not_active Withdrawn

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