Understanding Qualcomm's Snapdragon 810: Performance Preview

WTR3925

There are a few things that are important when talking about a transceiver. To recap, transceivers have a few key elements. On the receive side, we see the need for low noise amplifiers, down-converters, and narrow-band amplifiers. On the transmit side, we need a driver amplifier, up-converter, and another set of narrow-band amplifiers. While most of RF360 is built on relatively old process nodes for CMOS technology, the transceiver can be built on newer CMOS processes because it’s doesn’t have to handle the level of signal that the rest of the front end does.

At a high level, the WTR3925 really brings two new capabilities to the table. First, it does away with the need for a companion transceiver in order to achieve carrier aggregation, which the WTR1625L/WFR1620 combination provided. It seems that this is due to the need for additional ports on the transceiver, which the WTR1625L lacked. The other improvement is that WTR3925 moves to a new 28nm RF process, as opposed to the 65nm RF process used for the WTR1625L.

As a quick aside, RF processes are largely similar to CMOS processes, although with a few modifications. These changes can be thicker metal in interconnects between transistors and memcaps, which are analogous to capacitors in DRAM. Qualcomm claims that this will drive down power consumption, however this is a product of a new architecture that takes advantage of the smaller process node. Unlike digital logic such as what we see on the baseband, RF does not directly benefit from scaling to lower processes. In fact, there is a chance that scaling to lower process nodes can hurt power consumption because even though the transistor can operate faster, there is more noise As a result of this noise, the amplifiers in the transceivers may need more stages and more power in order to achieve the same noise figure.

MDM9x35

While baseband was previously one of the most popular topics in RF, as can be seen by this article RF is much more than just the baseband. However, the baseband is a critical part of the chain. The RF front end is critical for reception and a myriad of other issues, but feature support and control of the front-end lies with the baseband. The baseband must properly interpret the information that the front-end provides and also send out information to the front-end to transmit.

Fortunately, the baseband is implemented with digital logic, so there are significant benefits to moving to the latest and greatest CMOS process node. Lower voltage (and therefore power) is needed to drive the transistors, and it becomes easier to drive higher performance in the DSP. In the case of the MDM9x35, we see that there's a QDSP clocked at 800 MHz for modem functions, and a 1.2 GHz Cortex A7 for functions such as mobile hotspot.

In the case of MDM9x35, there are two major contributors to the reduction in power consumption. The first is the move from 28nm HPm to 20nm SoC. While 20nm SoC doesn’t utilize FinFET, we still see scaling in power, performance, and density. The other area where we see power savings is better implementation of various algorithms. As a result, we should see around 20-25% power savings with the same workload.

MDM9x45

In the time since the first MDM9x35 devices were launched, Qualcomm has also iterated on modems. With the 9x45 generation, we see a move to category 10 LTE, which includes 450 Mbps maximum download speed when aggregating three 20 MHz carriers, and two 20 MHz carriers on the uplink for a maximum of 100 Mbps. Although the Snapdragon 810 doesn't have a 9x45 IP block for the modem, the Snapdragon 810 does support up a maximum of 450 Mbps for download with category 9 LTE. However, there is no uplink carrier aggregation in such a scenario. Uplink carrier aggregation is only possible with category 7, which limits downlink speeds to 300 Mbps.

Qualcomm claims that the MDM9x45 should bring around 40% energy savings in an LTE carrier aggregation scenario when compared to the MDM9x25 modem. In addition, these new modems bring in a new generation of GNSS location, with support for EU's Galileo constellation. It's likely that the DSPs and other aspects of this modem have been beefed up relative to the 9x35 and 8994 modems to enable category 10 data rates.