viperpaki007
Full Member level 5
Hi,
Currently fast envelope tracking DC-DC converters used for envelope tracking applications use a combined parallel structure of switching and linear converter[1].
The operation of combined structure is something like this: When the modulation envelope voltage increases, linear amplifier follows it. Output current sensing circuit senses an increase in linear converter current and copies this current to switching amplifier. Output current of switching amplifier increases which eventually forces the linear amplifier to lower its output current due to unity gain feedback. In this way, both high efficiency and high bandwidth is achieved as most of the current is supplied by switching converter and linear converter provides the fast high bandwidth operation.
[1]
In the design guide-lines of the converter, it is suggested that linear converter output impedance should be as low as possible. However, if i make the linear converter output impedance low then after connecting linear and switching converter in parallel, most of the switching converter current sinks to linear converter output and does not go to load. Can anybody suggest what should be the right way to combine linear and switching converter in parallel.
[1] M.Hassan, "A combined series parallel hybrid envelope amplifier for envelope tracking mobile terminal RF power amplifier applications", IEEE journal Solid State Circuits 2012.
regards
Currently fast envelope tracking DC-DC converters used for envelope tracking applications use a combined parallel structure of switching and linear converter[1].
The operation of combined structure is something like this: When the modulation envelope voltage increases, linear amplifier follows it. Output current sensing circuit senses an increase in linear converter current and copies this current to switching amplifier. Output current of switching amplifier increases which eventually forces the linear amplifier to lower its output current due to unity gain feedback. In this way, both high efficiency and high bandwidth is achieved as most of the current is supplied by switching converter and linear converter provides the fast high bandwidth operation.
[1]
In the design guide-lines of the converter, it is suggested that linear converter output impedance should be as low as possible. However, if i make the linear converter output impedance low then after connecting linear and switching converter in parallel, most of the switching converter current sinks to linear converter output and does not go to load. Can anybody suggest what should be the right way to combine linear and switching converter in parallel.
[1] M.Hassan, "A combined series parallel hybrid envelope amplifier for envelope tracking mobile terminal RF power amplifier applications", IEEE journal Solid State Circuits 2012.
regards