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TABLE II. MEASURED EFFICIENCY OF THE IMPLEMENTED EER TRANSMITTER WHEN THE AMPLITUDE MODULATION IS APPLIED AND THE LINEAR REGULATOR IS SUPPLIED BY CONSTANT AND VARIABLE VOLTAGE

Table 1 II. MEASURED EFFICIENCY OF THE IMPLEMENTED EER TRANSMITTER WHEN THE AMPLITUDE MODULATION IS APPLIED AND THE LINEAR REGULATOR IS SUPPLIED BY CONSTANT AND VARIABLE VOLTAGE

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Figure 1. Block Scheme of Kahn Technique Transmitter where f is the carrier frequency, O(t) and I(t) are modulated signals. The block scheme of an EER system is shown in Figure 1.
Figure 1. Block Scheme of Kahn Technique Transmitter where f is the carrier frequency, O(t) and I(t) are modulated signals. The block scheme of an EER system is shown in Figure 1.
Figure 2. Simplified schematic of the proposed envelope amplifier The switching frequency of the MOSFETs that are inside the two-level cells will depend on the signal that is reproduced. If the signal is a sine wave of | MHz, the switching frequency of the multilevel converter 1s 1MHz as well. Therefore, with this topology high frequency signals can be reproduced by applying the switching frequency equal to the frequency of the signal, instead of several times higher, like in the case of PWM converters.
Figure 2. Simplified schematic of the proposed envelope amplifier The switching frequency of the MOSFETs that are inside the two-level cells will depend on the signal that is reproduced. If the signal is a sine wave of | MHz, the switching frequency of the multilevel converter 1s 1MHz as well. Therefore, with this topology high frequency signals can be reproduced by applying the switching frequency equal to the frequency of the signal, instead of several times higher, like in the case of PWM converters.
Figure 3. Time diagrams of the proposed envelope amplifier
Figure 3. Time diagrams of the proposed envelope amplifier
igure 4. Simplified schematic of the implemented envelope amplifier
igure 4. Simplified schematic of the implemented envelope amplifier
Figure 5. Output voltage of the multilevel converter and envelope amplifier when a 2MHz sine wave is reproduced The output voltages of the multilevel converter are selected by maximizing equation 3, while the MOSFET fot the pass element and operational amplifier in the linear regulator have been selected in the way to obtain high bandwidth of the envelope amplifier. The bandwidth of the selected operational amplifier (LM6172) is 100 MHz in oper loop, while the MOSFET (BLF177) is from HF/VHF power MOS family of transistors. The output voltages of the envelope amplifier and the multilevel converter in the case when a 2 MHz sine wave is reproduced are shown in Figure 5.
Figure 5. Output voltage of the multilevel converter and envelope amplifier when a 2MHz sine wave is reproduced The output voltages of the multilevel converter are selected by maximizing equation 3, while the MOSFET fot the pass element and operational amplifier in the linear regulator have been selected in the way to obtain high bandwidth of the envelope amplifier. The bandwidth of the selected operational amplifier (LM6172) is 100 MHz in oper loop, while the MOSFET (BLF177) is from HF/VHF power MOS family of transistors. The output voltages of the envelope amplifier and the multilevel converter in the case when a 2 MHz sine wave is reproduced are shown in Figure 5.
operates at 120MHz In [1] it has been explained that the bandwidth of the envelope amplifier has to be, at least, two times higher than the bandwidth of the RF signal. The reproduced envelope should not have any attenuation up to 2 MHz and it has been shown that the proposed envelope amplifier can reproduce 2 MHz sine wave of maximum amplitude. However, this does not mean that the implemented envelope amplifier cannot reproduce signals of wider bandwidth. The higher harmonics that are very important for high linearity of Kahn’s transmitter usually are of much smaller amplitudes than the maximum amplitude that can be reproduced by the envelope amplifier. Based on the analysis presented in [1], a test with rectified sine wave has been conducted. If the reference signal is a rectified sine wave of frequency f, its spectrum is infinite and consists of tones that are placed on frequencies 2f 4f 6f...A rectified 500 kHz sine wave of maximum amplitude has been used as the reference and the response of the envelope amplifier has been measured, Figure 10. The spectrum of the output signal is compared with the spectrum of the reference signal, Figure 11. It can be seen that the proposed envelope amplifier admits even the harmonic higher than 2 MHz.
operates at 120MHz In [1] it has been explained that the bandwidth of the envelope amplifier has to be, at least, two times higher than the bandwidth of the RF signal. The reproduced envelope should not have any attenuation up to 2 MHz and it has been shown that the proposed envelope amplifier can reproduce 2 MHz sine wave of maximum amplitude. However, this does not mean that the implemented envelope amplifier cannot reproduce signals of wider bandwidth. The higher harmonics that are very important for high linearity of Kahn’s transmitter usually are of much smaller amplitudes than the maximum amplitude that can be reproduced by the envelope amplifier. Based on the analysis presented in [1], a test with rectified sine wave has been conducted. If the reference signal is a rectified sine wave of frequency f, its spectrum is infinite and consists of tones that are placed on frequencies 2f 4f 6f...A rectified 500 kHz sine wave of maximum amplitude has been used as the reference and the response of the envelope amplifier has been measured, Figure 10. The spectrum of the output signal is compared with the spectrum of the reference signal, Figure 11. It can be seen that the proposed envelope amplifier admits even the harmonic higher than 2 MHz.
Figure 7. Measured output power and the efficiency of the implemented class E for different switching frequencies (instrument accuracy: 5%).
Figure 7. Measured output power and the efficiency of the implemented class E for different switching frequencies (instrument accuracy: 5%).
Figure 9. Attenuation of the intermodulaiton components measured by a spectral analyzer in the two tone test, when a sine waves of 1 MHz and 1.05 MHz are used. Figure 8. Output voltage of the multilevel converter and envelope amplifier when a two tone test is performed. Two tone signal consists of two sine waves of 200 kHz and 250kHz
Figure 9. Attenuation of the intermodulaiton components measured by a spectral analyzer in the two tone test, when a sine waves of 1 MHz and 1.05 MHz are used. Figure 8. Output voltage of the multilevel converter and envelope amplifier when a two tone test is performed. Two tone signal consists of two sine waves of 200 kHz and 250kHz
Figure 10. Waveform of multilevel’s output voltage and linear regulator’s output voltage when a rectified 500 kHz sine wave is used as the reference Figure 11. Spectrum of the reference and output signal when a rectified 500kHz sine wave is used as the reference. All the values are scaled to the de value of the signal
Figure 10. Waveform of multilevel’s output voltage and linear regulator’s output voltage when a rectified 500 kHz sine wave is used as the reference Figure 11. Spectrum of the reference and output signal when a rectified 500kHz sine wave is used as the reference. All the values are scaled to the de value of the signal
Figure 14 shows the relevant waveforms when a 2 MHz sine wave is used as the envelope reference. It can be observed hat the glitches in supply voltage of the class E converter are 1egligible. The supply voltage of the class E converter is Jelayed compared to the envelope amplifier’s output voltage Jue to the employed LC filter. Figure 12. Photogtaph of the implemented EER Transmitter (on the right) with FPGA board, A/D and D/A converters (on the left)
Figure 14 shows the relevant waveforms when a 2 MHz sine wave is used as the envelope reference. It can be observed hat the glitches in supply voltage of the class E converter are 1egligible. The supply voltage of the class E converter is Jelayed compared to the envelope amplifier’s output voltage Jue to the employed LC filter. Figure 12. Photogtaph of the implemented EER Transmitter (on the right) with FPGA board, A/D and D/A converters (on the left)
Figure 14. Oscilloscope waveforms of the multilevel’s output (label 1), envelope amplifier’s output (label 2), supply voltage of the class E amplifier (label 3) and the output of the implemented EER transmitter (label 4) when the envelope reference is a 2 MHz sine wave Figure 13. Oscilloscope waveforms of the envelope reference (label 1), multilevel’s output voltage (label 2), envelope’s amplifier output (label 3) and the EER transmitter’s output (label 4), when the envelope reference is a 500 kHz sinewave
Figure 14. Oscilloscope waveforms of the multilevel’s output (label 1), envelope amplifier’s output (label 2), supply voltage of the class E amplifier (label 3) and the output of the implemented EER transmitter (label 4) when the envelope reference is a 2 MHz sine wave Figure 13. Oscilloscope waveforms of the envelope reference (label 1), multilevel’s output voltage (label 2), envelope’s amplifier output (label 3) and the EER transmitter’s output (label 4), when the envelope reference is a 500 kHz sinewave
In order to measure the linearity of the complete EER transmitter a simple double-sideband suppressed-carrier (DSB-SC) transmission is performed, like in [1]. The carrier frequency is 125 MHz, while the modulated signal is 100 kHz sine wave. This corresponds to the reference that is composed of two tones, 124.9 MHz and 125.1 MHz respectively. The envelope reference is a rectified sine wave, while the phase changes for 180 degrees every time when the envelope reaches zero. Figure 16 shows the oscilloscope waveforms for this test. High frequency noise in the envelope reference can be clearly observed, and it can be seen that it is filtered by the linear regulator due to its finite bandwidth.
In order to measure the linearity of the complete EER transmitter a simple double-sideband suppressed-carrier (DSB-SC) transmission is performed, like in [1]. The carrier frequency is 125 MHz, while the modulated signal is 100 kHz sine wave. This corresponds to the reference that is composed of two tones, 124.9 MHz and 125.1 MHz respectively. The envelope reference is a rectified sine wave, while the phase changes for 180 degrees every time when the envelope reaches zero. Figure 16 shows the oscilloscope waveforms for this test. High frequency noise in the envelope reference can be clearly observed, and it can be seen that it is filtered by the linear regulator due to its finite bandwidth.
Figure 15. Oscilloscope waveforms of the envelope reference (label 1), multilevel’s output voltage (label 2), envelope amplifier’s output voltage (label 3) and the output of the implemented EER transmitter (label 4)when the reference signal is composed of two tones (200 kHZ and 250 kHz)
Figure 15. Oscilloscope waveforms of the envelope reference (label 1), multilevel’s output voltage (label 2), envelope amplifier’s output voltage (label 3) and the output of the implemented EER transmitter (label 4)when the reference signal is composed of two tones (200 kHZ and 250 kHz)
filter all the high harmonic from the input current. In order to supply the class E amplifier with variable voltage, this filter was changed, and this change lead to the detoriation of the efficiency. Figure 16. Oscilloscope waveforms of envelope reference (label 1), multilevel’s output voltage (label 2), envelope amplifier’s output (label 3) and the output of the implemented EER transmitter (label 4) when the transmitter’s refrence is a simple DSB-SC signal with carrier of 125 MHz and a 100 kHz sine wave as the modualted signal
filter all the high harmonic from the input current. In order to supply the class E amplifier with variable voltage, this filter was changed, and this change lead to the detoriation of the efficiency. Figure 16. Oscilloscope waveforms of envelope reference (label 1), multilevel’s output voltage (label 2), envelope amplifier’s output (label 3) and the output of the implemented EER transmitter (label 4) when the transmitter’s refrence is a simple DSB-SC signal with carrier of 125 MHz and a 100 kHz sine wave as the modualted signal
Figure 17. Spectrum of the transmitter’s output signal when the system’s reference is a simple DSB-SC signal with carrier of 125 MHz and a 100 kHz sine wave as the modualted signal
Figure 17. Spectrum of the transmitter’s output signal when the system’s reference is a simple DSB-SC signal with carrier of 125 MHz and a 100 kHz sine wave as the modualted signal
Related topics:
EngineeringElectrical EngineeringElectronic EngineeringPeak-to-Average power ratio (PAPR)Envelope Elimination and RestorationPhase ModulationMultilevel ConverterPower Added EfficiencyPeak to Average Power Ratio
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