Amplifier linearization
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From: desongyu on 14 May 2010 15:05 Hi, I am experimenting with the feedforward linearization technique for a amplifier with a specified AM/AM, AM/PM response. Could someone help to shed some light on the advantage of linearization? At first, I thought linearization allows IBO to be decreased so one can operate closer to saturation. Then I came to me that for high order modulations, i.e. 16APSK(2 circles of I/Q constellations), the Peak-to-avg-pwr ratio(PAPR) is really the determinant factor. For example, if we can backoff the amplifier at IBO -1dB with linearization but PAPR is 1.5dB, we still have to operate at IBO of -1.5dB... defeating the purpose of linearization... thank you for your help on this
From: Vladimir Vassilevsky on 14 May 2010 15:27 desongyu wrote: > Hi, > > I am experimenting with the feedforward linearization technique for a > amplifier with a specified AM/AM, AM/PM response. Could someone help to > shed some light on the advantage of linearization? At first, I thought > linearization allows IBO to be decreased so one can operate closer to > saturation. Then I came to me that for high order modulations, i.e. > 16APSK(2 circles of I/Q constellations), the Peak-to-avg-pwr ratio(PAPR) is > really the determinant factor. For example, if we can backoff the amplifier > at IBO -1dB with linearization but PAPR is 1.5dB, we still have to operate > at IBO of -1.5dB... defeating the purpose of linearization... > The PAPR is given to you. It is a property of the signal. Linearization is what you may have to do to cope with PAPR. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: cfy30 on 15 May 2010 12:12 You meant predistortion to linearize AM/AM and AM/PM, right? Feedforward refers to a two-loop scheme that involves extracting the error signal, adjusting its amplitude and phase in the first loop, and then inject it back in the second loop so as to linearize the amplifying system. The xdB PAPR doesn't dictate the amplifier needs to operate xdB below P1dB. You can always drive the PA harder to get better efficiency as long as EVM/RHO and ACPR are alright. In general, ACPR is the usually the bottleneck and needs to improve before EVM fails. cfy30 >Hi, > >I am experimenting with the feedforward linearization technique for a >amplifier with a specified AM/AM, AM/PM response. Could someone help to >shed some light on the advantage of linearization? At first, I thought >linearization allows IBO to be decreased so one can operate closer to >saturation. Then I came to me that for high order modulations, i.e. >16APSK(2 circles of I/Q constellations), the Peak-to-avg-pwr ratio(PAPR) is >really the determinant factor. For example, if we can backoff the amplifier >at IBO -1dB with linearization but PAPR is 1.5dB, we still have to operate >at IBO of -1.5dB... defeating the purpose of linearization... > >thank you for your help on this > > >
From: desongyu on 19 May 2010 14:19 Thank you everyone for your reply. I understand that the PAPR is the property of the signal; so with pulse shaping, 8PSK has a lower PAPR than 12-4APSK let's say(12-4 has 2 circles of constellation). But what I don't understand is what exactly linearization of the amplifier would buy if you are limited by your PAPR so your peak power out should not exceed 0dB output power, as shown on AM/AM. i.e. if IBO is 1dB, with linearization, PAPR could be 1.5dB. This is not possible without linearization since 0.5dB of the signal power would have exceeded amplifier's saturation output power. One thing I am thinking linearization buys is that it linearizes the AM/AM so you can get more output power, before saturation, when decreasing IBO. Please help with my understanding. Thank you for your expert advice. > >desongyu wrote: > >> Hi, >> >> I am experimenting with the feedforward linearization technique for a >> amplifier with a specified AM/AM, AM/PM response. Could someone help to >> shed some light on the advantage of linearization? At first, I thought >> linearization allows IBO to be decreased so one can operate closer to >> saturation. Then I came to me that for high order modulations, i.e. >> 16APSK(2 circles of I/Q constellations), the Peak-to-avg-pwr ratio(PAPR) is >> really the determinant factor. For example, if we can backoff the amplifier >> at IBO -1dB with linearization but PAPR is 1.5dB, we still have to operate >> at IBO of -1.5dB... defeating the purpose of linearization... >> > >The PAPR is given to you. It is a property of the signal. Linearization >is what you may have to do to cope with PAPR. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com > >
From: cfy30 on 20 May 2010 01:29
The goal of linearization is to improve linearity(AM/AM, AM/PM, ACPR, EVM) and drive the PA harder for better PAE. Linerization can be achieved by RF feedforward technique, analog/baseband/digital predistortion or a combination of both predistortion and feedforward. In the last few years, most of the research focus is on envelope tracking, and envelope elimination and restoration. Broadly speaking, they are also linearization techniques. cfy30 >Thank you everyone for your reply. I understand that the PAPR is the >property of the signal; so with pulse shaping, 8PSK has a lower PAPR than >12-4APSK let's say(12-4 has 2 circles of constellation). But what I don't >understand is what exactly linearization of the amplifier would buy if you >are limited by your PAPR so your peak power out should not exceed 0dB >output power, as shown on AM/AM. >i.e. if IBO is 1dB, with linearization, PAPR could be 1.5dB. This is not >possible without linearization since 0.5dB of the signal power would have >exceeded amplifier's saturation output power. > >One thing I am thinking linearization buys is that it linearizes the AM/AM >so you can get more output power, before saturation, when decreasing IBO. > >Please help with my understanding. Thank you for your expert advice. > >> >>desongyu wrote: >> >>> Hi, >>> >>> I am experimenting with the feedforward linearization technique for a >>> amplifier with a specified AM/AM, AM/PM response. Could someone help to >>> shed some light on the advantage of linearization? At first, I thought >>> linearization allows IBO to be decreased so one can operate closer to >>> saturation. Then I came to me that for high order modulations, i.e. >>> 16APSK(2 circles of I/Q constellations), the Peak-to-avg-pwr ratio(PAPR) >is >>> really the determinant factor. For example, if we can backoff the >amplifier >>> at IBO -1dB with linearization but PAPR is 1.5dB, we still have to >operate >>> at IBO of -1.5dB... defeating the purpose of linearization... >>> >> >>The PAPR is given to you. It is a property of the signal. Linearization >>is what you may have to do to cope with PAPR. >> >> >>Vladimir Vassilevsky >>DSP and Mixed Signal Design Consultant >>http://www.abvolt.com >> >> > |