GB2501524A - An efficient asymmetric push-pull amplifier for an envelope modulator - Google Patents

An efficient asymmetric push-pull amplifier for an envelope modulator Download PDF

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Publication number
GB2501524A
GB2501524A GB201207389A GB201207389A GB2501524A GB 2501524 A GB2501524 A GB 2501524A GB 201207389 A GB201207389 A GB 201207389A GB 201207389 A GB201207389 A GB 201207389A GB 2501524 A GB2501524 A GB 2501524A
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Prior art keywords
transformer
winding
input
coupled
output
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GB201207389D0 (en
Inventor
Gavin Watkins
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Toshiba Europe Ltd
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Toshiba Research Europe Ltd
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Priority to GB201207389A priority Critical patent/GB2501524A/en
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Publication of GB2501524A publication Critical patent/GB2501524A/en
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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
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
    • H03F1/0216—Continuous control
    • H03F1/0222—Continuous control by using a signal derived from the input signal
    • 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
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
    • H03F1/0216—Continuous control
    • H03F1/0222—Continuous control by using a signal derived from the input signal
    • H03F1/0227—Continuous control by using a signal derived from the input signal using supply converters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/189—High frequency amplifiers, e.g. radio frequency amplifiers
    • H03F3/19—High frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only
    • H03F3/193—High frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only with field-effect devices
    • H03F3/1935—High frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only with field-effect devices with junction-FET devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
    • H03F3/211—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only using a combination of several amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
    • H03F3/245—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages with semiconductor devices only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/26—Push-pull amplifiers; Phase-splitters therefor
    • H03F3/265—Push-pull amplifiers; Phase-splitters therefor with field-effect transistors only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/102—A non-specified detector of a signal envelope being used in an amplifying circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/255—Amplifier input adaptation especially for transmission line coupling purposes, e.g. impedance adaptation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/426—Indexing scheme relating to amplifiers the amplifier comprising circuitry for protection against overload
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/432—Two or more amplifiers of different type are coupled in parallel at the input or output, e.g. a class D and a linear amplifier, a class B and a class A amplifier

Abstract

An efficient asymmetric push-pull amplifier for an envelope modulator because the positive peaks of the AC component of an envelope signal in an LTE or DVT-T2 system are greater than the negative peaks (figure 8), the efficiency of a push-pull amplifier for the AC part of an envelope modulator (306, figure 7) may be improved by asymmetry in the turns of the input transformer. Inequality of the turns B and C allows both the transistors Q1 and Q2 to saturate at the same given input AC peak-to-peak amplitude despite the asymmetric input signal at terminal 112. The ratio of the turns D and E in the output transformer is the same as that between B and C. The input and output transformers may both be transmission-line transformers.

Description

Amplifier
FIELD
Embodiments described herein relate generally to transformer coupled push-pull amplifiers.
BACKGROUND
A conventional transformer coupled push-pull amplifier uses a centre4apped input transformer to produce opposite polarity signals which are fed to two transistors. One of the transistors is arranged to amplify the positive excursions of an input signal and the second transistor is arranged to amplify the negative excursions of the input signal.
A second centre-tapped transformer on the output side is used to recombine the two amplified signals and to drive a load.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows a transformer coupled push-pull amplifier according to an embodiment; Figure 2 shows an asymmetric input signal with different amplitude positive and negative excursions; Figure 3 shows drain voltage and drain current for a field effect transistor in a transformer coupled push-pull amplifier according to an embodiment; Figure 4 shows drain voltage of a field effect transistor in a transformer coupled push-pull amplifier having unequal windings on transformers according to an embodiment compared with drain voltage of a field effect transistor in a transformer coupled push-pull amplifier having equal windings on transformers; Figure 5 shows current for a field effect transistor in a transformer coupled push-pull amplifier having unequal windings on transformers according to an embodiment compared with drain current for a field effect transistor in a transformer coupled push-pull amplifier having equal windings on transformers; 5.
Figure 6 shows a transformer coupled push-pull amplifier according to an embodiment; Figure 7 shows an envelope modulated power amplifier system according to an embodiment.
DETAILED DESCRIPTION
In an embodiment, a transformer coupled push-pull amplifier comprises a first input terminal and a second input terminal; an input transformer configured to couple to an input signal applied to the first and second input terminals, the input transformer comprising a first winding and a second winding, the first winding comprising a conductor wound through a first number of turns and the second winding comprising a conductor wound through a second number of turns, the first number being different from the second number; a first amplifying element coupled to the first winding, the first amplifying element configured to amplify parts of the input signal having a higher voltage on the first input terminal than on the second input terminal; a second amplifying element coupled to the second winding, the second amplifying element configured to amplify parts of the input signal having a higher voltage on the second input terminal than on the first input terminal; and an output transformer coupled to the first amplifying element and the second amplifying elment and configured to drive a load.
In an embodiment, the input signal is an asymmetric signal having a maximum excursion when the voltage on the first input terminal is higher than the voltage on the second input terminal which is greater than a maximum excursion when the voltage on the second input terminal is higher than the voltage on the first input terminal.
In an embodiment, the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding comprising a conductor wound through a fourth number of turns, the third number being different from the fourth number, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element.
In an embodiment, the ratio of the first number to the second number is substantially equal to the ratio of the third number to fourth number..
In an embodiment, the ratio of the first number to the second number is selected according to the ratio of a maximum excursion of the input signal when the voltage on the first input terminal is higher than the voltage on the second input terminal to a maximum excursion of the input signal when the voltage on the second input terminal is higher than the voltage on the first input terminal, In an embodiment, the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding coupled comprising a conductor wound through a fourth number of turns, the third number being different from the fourth number, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element, and wherein the ratio of the third number to the Iourth number is selected according to the ratio of the of a maximum excursion of the input signal when the voltage on the first input terminal is higher than the voltage on the second input terminal to a maximum excursion of the input signal when the voltage on the second input terminal is higher than the voltage on the first input terminal.
In an embodiment, the input transformer and the output transformer are flux coupled transformers.
In an embodiment1 the input transformer comprises a primary winding configured to receive the input signal and a secondary winding, wherein the secondary winding comprises the first winding and the second winding.
In an embodiment, the input transformer and the output transformer are transmission line transformers.
In an embodiment, the first amplifying element and / or the second amplifying element are transistors.
In an embodiment, the first amplifying element and / or the second amplifying element
are field effect transistors.
In an embodiment, the second number is at least 10 percent greater than the first number.
In an embodiment, the second number is at least 20 percent greater than the first number.
In an embodiment, the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding comprising a conductor wound through a fourth number of turns, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element and the fourth number is at least 10 percent greater than the third number.
In an embodiment, the fourth number is at least 20 percent greater than the third number.
In an embodiment an envelope modulator comprises a transformer coupled push-pull amplifier comprising an input transformer configured to couple to an alternating current input signal; a first amplifying element configured to amplify pads of the alternating current input signet having a first polarity; a second amplifying element configured to amplify parts of the alternating current input signal having a second polarity; and an output transformer, wherein the input transformer comprises a first winding coupled to the first amplifying element and a second winding coupled to the second amplifying element and the first winding and the second winding have an unequal number of turns.
In an embodiment an envelope modulated power amplifier system comprises a power amplifier configured to amplify an input signal; an envelope detector configured to detect an envelope of the input signal; and a transformer coupled push-pull amplifier comprising an input transformer configured to couple to an alternating current input signal; a first amplifying element configured to amplify parts of the alternating current input signal having a first polarity; a second amplifying element configured to amplify parts of the alternating current input signal having a second polarity; and an output transformer, wherein the input transformer comprises a first winding coupled to the first amplifying element and a second winding coupled to the second amplifying element and the first winding and the second winding have an unequal number of turns, configured to provide a supply voltage to the power amplifier, wherein the alternating current input signal of the transformer coupled push-pull amplifier is an alternating current component of the envelope detected by the envelope detector.
Figure 1 shows a transformer coupled push-pull amplifier 100 according to an embodiment. The transformer coupled push-pull amplifier 100 comprises an input transformer Ti, an output transformer 12, a first field effect transistor Qi and a second field effect transistor 02. In this embodiment, the first transformer and the second transformer are flux coupled transformers. The transformer coupled transformer coupled push-pull amplifier 100 is configured to amplify an input signal yin which is across a ground input terminal 110 and a signal input terminal 112. The ground input terminal 110 and the signal input terminal 112 are connected across the primary winding of the input transformer Ti. The primary winding of the input transformer Ti has a number of turns A. The secondary winding of the input transformer Ti is divided into two parts. A connection from between the two parts is connected to ground. This may be considered as atap of the primary winding. The tap divides the secondary winding into a first winding part having a number of turns B and a second winding part having a number of turns C. The first winding part and the second winding part have an unequal number of turns. The first winding part of the second winding of the input transformer Ti is connected to the gate terminal of the first field effect transistor 01. The second winding part of the secondary winding of the input transformer Ti is connected to the gate terminal of the second field effect transistor Q2.
The output transformer T2 has a primary winding with a tap connected to the supply voltage +VDD of the transformer coupled push-pull amplifier 100. The tap divides the primary winding of the output transformer T2 into a first winding part and a second winding part. The first winding part of the primary winding of the output transformer T2 has a number of turns 0. The second winding part of the primary winding of the output transformer 12 has a number of turns E. The first winding part and the second winding part have an unequal number of turns.
The ratio B/C of the number of turns on the first winding part to the number of turns on the second winding of the secondary winding of the input transistor is equal to the ratio DIE of the number of turns on the first winding part to the number of turns on the second winding of the primary winding of the output transformer T2.
The first winding part of the primary winding of the output transformer T2 is connected to the drain terminal of the first field effect transistor 01. The second winding part of the primary winding of the output transformer T2 is connected to the drain terminal of the second field effect transistor 02. The source terminals of the first field effect transistor 01 and the second field effect transistor 02 are connected to ground.
The secondary winding of the output transformer T2 has a number of turns F and is connected across a load RL over which the amplified output voltage Vout is applied.
According to this embodiment, by having a different number of turns on the first and second winding parts of the input and output transformers, the efficiency of the amplifier when amplifying an asymmetric signal is increased.
In an embodiment, the field effect transistors are metal-oxide-semiconductor field effect transistors (MOSFETs).
In an alternative embodiment transistors such as bipolar transistors are used as amplifying elements in place of the field effect transistors. In a further embodiment.
other amplifying elements such as thermionic valves are used.
Conventional transformer coupled push-pull amplifiers are designed for use with signals which have equal amplitude positive and negative signal excursions, for example sinusoidal waves, Under these conditions both positive and negative peaks approach the supply rail. This is not the case for an asymmetric signal.
Figure 2 shows an example of an asymmetric signal. The positive excursions of the signal shown in figure 2 reach a higher voltage that the negative excursions.
An example of an asymmetric signal such as that shown in Figure 2 is the AC component of a 3GPP Long Term Evolution (LTE) envelope signal. The AC component of an LTE envelope signal has positive excursions, or peaks, that are approximately 50% larger than the negative excursions, or nulls. This is described in more detail with reference to Figure 8 below.
Figure 3 shows the drain voltage and current waveforms for the first field effect transistor Qi. The drain voltage of Qi uses the full voltage swing between VDD and ground. Here, Q1 is configured to arrange the positive excursions of the input signal.
Figure 4 shows a comparison of the drain voltage for the second field effect transistor Q2 with equal and unequal numbers of turns on the first and second winding parts of the input and output transformers. Here, Q2 is arranged to amplify the negative excursions of the input signal.
In the case where the first and second winding pads of the secondary winding of the input transformer have an equal number of turns and the first and second winding parts of the primary winding of the output transformer have an equal number of turns, there is a wasted voltage drop as shown in Figure 4. In this case, the full range of voltages between VDD and ground are not used.
In the case where an unequal number of turns are used on the windings, there is no wasted voltage drop as shown in Figure 4. The number of turns on the negative side that is the second winding part, C on Ti is greater than the number of turns on the first winding pad, B. By increasing the number of turns on the negative side, the voltage swing on the gate terminal second field effect transistor Q2 is increased. This means that the second field effect transistor can make use of the full voltage swing of the supply voltage. Since the second winding part of the primary winding of the output transformer T2 has more turns that the first winding part, the current flowing through the second winding part will be smaller for a given voltage drop.
In an embodiment, the winding A and the winding B showing in Figure 1 have 20 turns and the winding C has 30 turns, In such an embodiment, the second winding would have 50% more turns that the first winding. Thus the ratio would correspond to the ratio of the maximum positive excursion to the maximum negative excursion of the input signal shown in Figure 2. Those of skill in the art will appreciate that the number of turns on the windings may be varied. Embodiments are envisaged with a wide variety of numbers of turns on the windings from 20 to 20,000. As described above, it is the ratios of the numbers of turns that is selected and controlled.
Figure 5 shows the drain and mean current of 02 with equal and non-equal numbers of transformer turns. As shown in Figure 5, increasing the magnitude of the negative excursions reduces the current peaks flowing through Q2. The mean current is therefore also reduced by a proportional amount as shown in Figure 6.
As shown in Figure 5, matching the ratios of respectively, the numbers of turns on the first and second winding parts of the secondary winding of the input transformer, and the numbers of turns on the first and second winding parts of the primary winding of the output transformer reduces the overall power consumption since the full supply voltage range can be used by the circuit parts that amplify both the positive and the negative excursions.
Figure 6 shows *a transformer coupled push-pull amplifier 200 according to an embodiment. The transformer coupled push-pull amplifier 200 comprises an input transformer T3, an output transformer T3, a first field effect transistor 03 and a second field effect transistor 04. In this embodiment, the first transformer and the second transformer are transmission line transformers. The transformer coupled push pull amplifier 200 is configured to amplify an input signal yin which input across a ground input terminal 210 and a signal input terminal 212. In this embodiment the signal input 212 is connected to a first winding of the input transformer which has a number G of turns and the ground input terminal 210 is connected to a second winding of the input transformer which has a number of turns F-I. The number of turns C on the first winding of the input transistor and the number of turns H on the second winding of the input transformer are unequal.
The first winding of the input transformer is connected to the gate terminal of the first field effect transistor Q3. The second winding of the input transformer 13 is connected to the gate terminal of the second field, effect transistor 04. A first inductor Li is connected between the supply voltage +VDD and the drain terminal of the first field effect transistor 93. A second inductor L2 is connected between the supply voltage +VDD and the source terminal of the second field effect transistor 94. The source terminals of the first field effect transistor 03 and the second field effect transistor 04 are connected to ground.
The drain terminal of the first field effect transistor 03 is connected to a first winding of the output transformer T4 via a first capacitor Cl. The first winding of the output transformer 14 has a number of turns I. The source terminal of the second field effect transistor 04 is connected via a second capacitor C2 to a second winding of the output transformer 14. The second winding of the output transformer 14 has a number of turns J. A load is connected across the first and second windings of the output transformer T4. An output voltage Vout is output across the load. The number of turns I on the first winding of the output transformer T4 and the number of turns J on the second winding of the output transformer T4 are unequal.
The ratio C/H of the number of turns on the first winding to the number of turns on the second winding of the input transformer T3 is equal to the ratio lid of the number of turns on the first winding to the number of turns on the second winding the output transformer T4. -As described above in relation to the embodiment shown in Figure 1 the ratio the number of turns on the second windings to the number of turns on the first windings is selected to be equal to the ratio of the maximum positive excursions to the maximum negative excursions.
The ratio may be selected so that the number of turns on the second windings is 10 percent greater than the number of turns on the first winding. The ratio may be selected so that the number of turns on the second windings is 20 percent greater than the number of turns on the first windings.
It is envisaged that the transformer coupled push pull amplifier 100 shown in Figure 1 could be used with relatively low frequencies, for example in the audio range to relatively high frequencies in the radio frequency range. The transformer coupled push pull amplifier 200 shown in Figure 6 would be more suitable for operation in the radio frequency range than in the audio frequency range because of the presence of the two inductors Li and L2. At low frequencies, large inductors would be required.
Figure 7 shows an envelope modulated power amplifier system 300 according to an embodiment. The power amplifier system has an input 302 configured to receive a signal to be amplified. An envelope detector 304 detects the envelope of the input signal. The envelope signal is split into a direct current (DC) component and an alternating current (AC) component. The direct current component is amplified by a DC amplifier 306 and the alternating current component is amplified by an AC ampkfier 30& The AC amplifier 308 comprises a transformer coupled push pull amplifier as is described above. The amplified AC and DC components are combined and used to control the supply voltage of a power amplifier 310. The power amplifier 310 amplifies the input signal and provides an output to an output terminal 312.
Figure 8 shows an example of the envelope signal discussed above. The envelope signal has a DC component which is illustrated in Figure 8. if the DC component is subtracted from the envelope signal, the remaining AC component corresponds to the input signal shown in Figure 2.
In an embodiment, the envelope signal may be split into three components: one of the AC components being amplified a transformer coupled push pull amplifier as described above, and the second AC component being amplified by a second amplifying circuit.
In an embodiment, the DC and mid band components are amplified by a conventional dual-band envelope modulator and the upper frequency band is amplified by a transformer coupled push pull amplifier as described above.
In an embodiment a digital video transmitter comprises an envelope modulated power amplifier system as described in relation to Figure 7. The digital video transmitter may be a DVT-T2 transmitter.
In an embodiment a base station comprises an envelope modulated power ampHfier system as described in relation to Figure L The base station may be a LTE 20MHz bandwidth base station.
In the case of an asymmetric LTE envelope signal, in a tn-band split radio frequency envelope modulated power amplifier, the upper band amplifier typically would supply approximately 10% of the envelope energy. Due to the low efficiency of high frequency amplifiers, the high band amplifier is responsible for about 25% of the power consumption. By using a different number of turns on each half of the input and output transformers, both positive and negative excursions can be brought close to the supply rail. This reduces power consumption of the high band amplifier by approximately 27 %. It is envisaged that an overall efficiency increase of approximately 8% could be achieved by the use of an unequal transformer winding ratio as described.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel circuits described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes may be made without departing from the spirit of the inventions.
The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims (17)

  1. CLAIMS: 1. A transformer coupled push-pull amplifier comprising a first input terminal and a second input terminal; an input transformer configured to couple to an input signal applied to the first and second input terminals, the input transformer comprising a first winding and a second winding, the first winding comprising a conductor wound through a first number of turns and the second winding comprising a conductor wound through a second number of turns, the first number being different from the second number; a first amplifying element coupled to the first winding, the first amplifying element configured to amplify parts of the input signal having a higher voltage on the first input terminal than on the second input terminal; a second amplifying element coupled to the second winding, the second amplifying element configured to amplify parts of the input signal having a higher voltage on the second input terminal than on the first input temlinal; and an output transformer coupled to the first amplifying element and the second amplifying element and configured to drive a load.
  2. 2. A transformer coupled push-pull amplifier according to claim 1, wherein the input signal is an asymmetric signal having a maximum excursion when the voltage on the first input terminal is higher than the voltage on the second input terminal which is greater than a maximum excursion when the voltage on the second input terminal is higher than the voltage on the first input terminal.
  3. 3. A transformer coupled push-pull amplifier according to claim 1, wherein the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding comprising a conductor wound through a fourth number of turns, the third number being different from the fourth number, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element.
  4. 4. A transformer coupled push-pull amplifier according to claim 3 wherein the ratio of the first number to the second number is substantially equal to the ratio of the third number to fourth number.
  5. 5. A transformer coupled amplifier according claim 1, wherein the ratio of the first number to the second number is selected according to the ratio of a maximum excursion of the input signal when the voltage on the first input terminal is higher than the voltage on the second input terminal to a maximum excursion of the input signal when the voltage on the second input terminal is higher than the voltage on the first input terminal.
  6. 6. A transformer coupled amplifier according claim 5, wherein the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding coupled comprising a conductor wound through a fourth number of turns, the third number being different from the fourth number, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element, and wherein the ratio of the third number to the fourth number is selected according to the ratio of the of a maximum excursion of the input signal when the voltage on the first input terminal is higher than the voltage on the second input terminal to a maximum excursion of the input signal when the voltage on the second input terminal is higher than the voltage on the first input terminal.
  7. 7. A transformer coupled push-pull amplifier according to claim 1, wherein the input transformer and the output transformer are flux coupled transformers.
  8. 8. A transformer coupled push-pull amplifier according to claim 7, wherein the input transformer comprises a primary winding configured to receive the input signal and a secondary winding, wherein the secondary winding comprises the first winding and the second winding.
  9. 9. A transformer coupled push-pull amplifier according to claim 1, wherein the input transformer and the output transformer are transmission line transformers.
  10. 10. A transformer coupled push-pull amplifier according to claim 1, wherein the first amplifying element and I or the second amplifying element are transistors.
  11. 11. A transformer coupled push-pull amplifier according to claim 10, wherein the first amplifying element and I or the second amplifying element are field effect transistors.
  12. 12. A transformer coupled push-pull amplifier according to claim 1 wherein the second number is at least 10 percent greater than the first number.
  13. 13. A transformer coupled push-pull amplifier according to claim 12 wherein the second number is at least 20 percent greater than the first number.
  14. 14. A transformer coupled push-pull amplifier according to claim 12 wherein the output transformer comprises a first winding comprising a conductor wound through a third number of turns and a second winding comprising a conductor wound through a fourth number of turns, the first winding of the output transformer being coupled to the output of the first amplifying element and the second winding of the output transformer being coupled to the output of the second amplifying element and the fourth number is at least 10 percent greater than the third number.
  15. 15. A transformer coupled push-pull amplifier according to claim 14 wherein the fourth number is at least 20 percent greater than the third number.
  16. 16. An envelope modulator comprising a transformer coupled push pull amplifier according to claim 1.
  17. 17. An envelope modulated power amplifier system comprising a power amplifier configured to amplify an input signal; an envelope detector configured to detect an envelope of the input signal; and a transformer coupled push-pull amplifier according to claim 1 configured to provide a supply voltage to the power amplifier, wherein the alternating current input signal of the transformer coupled push-pull amplifier is an alternating current component of the envelope detected by the envelope detector.
GB201207389A 2012-04-26 2012-04-26 An efficient asymmetric push-pull amplifier for an envelope modulator Withdrawn GB2501524A (en)

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Publication number Priority date Publication date Assignee Title
US3066188A (en) * 1959-08-14 1962-11-27 Bendix Corp Unbalanced autotransformer audio amplifier
US3478274A (en) * 1967-09-11 1969-11-11 Bendix Corp Push-pull amplifier with asymmetrical drive and load
US3743954A (en) * 1971-04-14 1973-07-03 Patelhold Patentverwertung High power modulator-dimodulator amplifier circuit
GB2479166A (en) * 2010-03-30 2011-10-05 Nujira Ltd Supply voltage selection

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3066188A (en) * 1959-08-14 1962-11-27 Bendix Corp Unbalanced autotransformer audio amplifier
US3478274A (en) * 1967-09-11 1969-11-11 Bendix Corp Push-pull amplifier with asymmetrical drive and load
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GB2479166A (en) * 2010-03-30 2011-10-05 Nujira Ltd Supply voltage selection

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