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Industry view: Strategy Analytics on the RF market
Kristin Lewotsky
7/17/2012 5:03 PM EDT
Analog challenges
KL: What are the challenges on the analog side?
CT: With high frequency analog bits, you have to worry about the drive current and noise performance. You need low noise amplifiers, for example. As they make the transistors smaller and smaller, you lose drive capability, you're running at lower voltages, you have higher noise you have more problems with margins. It's not that it can't be done, it’s just really challenging and RF doesn't really scale the same way that digital scales.
KL: What major trends do you see?
CT: We’re seeing more and more digital content in the transceiver. We’re not yet at the point where we can do an analog to digital conversion at the antenna but we’re getting close. On the receive side, it's feasible to do almost everything in digital but on the transmit side you have power amplifiers where you have to match the output of the transceiver to a 50 ohm high-power environment.
You also need to protect the receive side from the transmit side. Typically, for the receiver, you need to knock any interfering signals from the transmit side down to -130 to -140 dB. That means you need filters with very specific RF frequencies corresponding to the different bands and very steep skirts. This gets to the challenge of the rest of what's in the handset—not the chipset but the RF front end. In a typical phone now you have eight or more bands, and eight bands is going to go to 16 with LTE. You’ve got a lot of different frequencies and you need to maintain coexistence and prevent interference, what Steve Mollenkopf of Qualcomm calls self jamming.
KL: Now, when you’re doing this much filtering the first thing I think of is loss. No matter how good your filters are, you're losing some your signal.
CT: Absolutely, you have insertion loss for the filters, which means you have to crank the power up and there's another trade-off—if you put all these bands into the phone with all the filters and switches your battery life will take a hit. You can make a very simple handset with a single band that does nothing but voice calls or you can put together a modern smartphone that does everything but bake quiche and then you're going to need a bigger battery.
KL: And the losses generate heat, and then you’ve got a thermal management problem.
CT: The operators and the OEM handset makers don't always have full appreciation of the limits. They’ll go to the chipset and power amp guys and say, ‘We want X, why can’t you deliver this?’ and it’s physically impossible. I don't have any statistics on this but certainly we hear all the time anecdotes from operators that users complain that their handsets just get too hot.
KL: What’s on the horizon for competing technologies?
CT: As far as doing D/A on the transmit side, I don't think they've figured out how to do well. There’s a lot of research going on in so-called digital PAs but those are really anywhere near feasible or practical yet—if they can be done, they can’t be done cost effectively. On the receive side, we’re not there yet but the A/D conversion can be done fairly close to the antenna, usually after the low noise amplifier. If you do put a converter right at the antenna, with today's technology it just draws too much current. You could do it in a base station if you wanted to but it's not really practical today for handsets.
KL: What keeps your customers up at night?
CT: Concerns about where they should spend their R&D dollars to stay competitive. Some of things we’re looking at specifically in handsets are multimode, multiband power amplifiers. Those are power amplifiers that can handle more than one air interface at once so instead of having a separate power amp for edge and wideband CDMA, you can now have a power amp that can do both.
When you're talking about a handset that has eight cellular bands, until recently that required eight separate power amplifiers which takes up an awful lot of space. If you collapse that into let's say two—one for the high bands and one for the low bands—then that's pretty attractive to the handset makers.
KL: How much activity is going on there?
CT: In December 2011, we estimated that shipments of multimode PAs were around $140 million in 2011, which is really significant considering that the year before they were maybe only $25 million. It’s a hot area right now and envelope tracking will be a part of it. I’m working on a report now on envelope tracking. Most people in the cell phone industry agree that this is coming sooner or later and it's a way to improve efficiency of the power amplifiers. It's something that will probably offered by the chipset makers but it has to work with PAs, so it's got to be cooperative. The chipset guys generally call the shots but the PA guys will have to develop and market power amplifiers that work with whatever the chipset guys do.
KL: What are the challenges on the analog side?
CT: With high frequency analog bits, you have to worry about the drive current and noise performance. You need low noise amplifiers, for example. As they make the transistors smaller and smaller, you lose drive capability, you're running at lower voltages, you have higher noise you have more problems with margins. It's not that it can't be done, it’s just really challenging and RF doesn't really scale the same way that digital scales.
KL: What major trends do you see?
CT: We’re seeing more and more digital content in the transceiver. We’re not yet at the point where we can do an analog to digital conversion at the antenna but we’re getting close. On the receive side, it's feasible to do almost everything in digital but on the transmit side you have power amplifiers where you have to match the output of the transceiver to a 50 ohm high-power environment.
You also need to protect the receive side from the transmit side. Typically, for the receiver, you need to knock any interfering signals from the transmit side down to -130 to -140 dB. That means you need filters with very specific RF frequencies corresponding to the different bands and very steep skirts. This gets to the challenge of the rest of what's in the handset—not the chipset but the RF front end. In a typical phone now you have eight or more bands, and eight bands is going to go to 16 with LTE. You’ve got a lot of different frequencies and you need to maintain coexistence and prevent interference, what Steve Mollenkopf of Qualcomm calls self jamming.
KL: Now, when you’re doing this much filtering the first thing I think of is loss. No matter how good your filters are, you're losing some your signal.
CT: Absolutely, you have insertion loss for the filters, which means you have to crank the power up and there's another trade-off—if you put all these bands into the phone with all the filters and switches your battery life will take a hit. You can make a very simple handset with a single band that does nothing but voice calls or you can put together a modern smartphone that does everything but bake quiche and then you're going to need a bigger battery.
KL: And the losses generate heat, and then you’ve got a thermal management problem.
CT: The operators and the OEM handset makers don't always have full appreciation of the limits. They’ll go to the chipset and power amp guys and say, ‘We want X, why can’t you deliver this?’ and it’s physically impossible. I don't have any statistics on this but certainly we hear all the time anecdotes from operators that users complain that their handsets just get too hot.
KL: What’s on the horizon for competing technologies?
CT: As far as doing D/A on the transmit side, I don't think they've figured out how to do well. There’s a lot of research going on in so-called digital PAs but those are really anywhere near feasible or practical yet—if they can be done, they can’t be done cost effectively. On the receive side, we’re not there yet but the A/D conversion can be done fairly close to the antenna, usually after the low noise amplifier. If you do put a converter right at the antenna, with today's technology it just draws too much current. You could do it in a base station if you wanted to but it's not really practical today for handsets.
KL: What keeps your customers up at night?
CT: Concerns about where they should spend their R&D dollars to stay competitive. Some of things we’re looking at specifically in handsets are multimode, multiband power amplifiers. Those are power amplifiers that can handle more than one air interface at once so instead of having a separate power amp for edge and wideband CDMA, you can now have a power amp that can do both.
When you're talking about a handset that has eight cellular bands, until recently that required eight separate power amplifiers which takes up an awful lot of space. If you collapse that into let's say two—one for the high bands and one for the low bands—then that's pretty attractive to the handset makers.
KL: How much activity is going on there?
CT: In December 2011, we estimated that shipments of multimode PAs were around $140 million in 2011, which is really significant considering that the year before they were maybe only $25 million. It’s a hot area right now and envelope tracking will be a part of it. I’m working on a report now on envelope tracking. Most people in the cell phone industry agree that this is coming sooner or later and it's a way to improve efficiency of the power amplifiers. It's something that will probably offered by the chipset makers but it has to work with PAs, so it's got to be cooperative. The chipset guys generally call the shots but the PA guys will have to develop and market power amplifiers that work with whatever the chipset guys do.
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