Atmel designs powerline controller with Cortex-M4
Atmel has announced an ARM-based system chip for smart meters that use power line communications (PLC) to talk to the outside world.
Low unpredictable impedances, multiple interference sources, and many nodes on the same local grid make ‘last mile’ communication between meters and a data concentrator over power cables a tough nut to crack.
The PRIME (PoweRline Intelligent Metering Evolution) Alliance’s solution is to use robust but computationally-intensive OFDM (orthogonal frequency division multiplexing) modulation to squeeze up to 130kbit/s onto carriers between 45kHz and 90kHz – part of the 3-95kHz ‘CENELEC-A’ band.
“Power line communications needs a more powerful processor because the protocol is quite complex. It has a complex stack and needs to be fully connected to application layers, which takes lots of memory,” Atmel marketing director, Jesus Teijeiro told Electronics Weekly.
To meet these needs, the firm has integrated a 120MHz ARM Cortex-M4, hardware accelerators, 2Mbyte of flash, and 160kbyte of SRAM into its chip – the ATSAM4SP32A.
It has also integrated a Class-D driver stage, which works with two off-chip mosfets to complete an output stage capable of forcing signals into the mains cable.
“With Class-D and OFDM, efficiency is 65%. If the output was linear, it would be 15-20%. The complete implementation including power amplifier is 750mW,” said Teijeiro, claiming this is the lowest dissipation yet announced.
750mW is for reading the meter every 15 minutes, which Teijeiro said is likely to allow utility companies to add at least 1% efficiency to a national power grid. “If you want to read every two months, power will be less than 750mW,” he added.
Why not integrate the mosfets? “Some people have the line-driver on chip, but that is a lot of power to dissipate on a chip that needs long life” said Teijeiro.
Two complete functional blocks have been left off the chip: power measurement (known as metrology in metering) and a display driver.
“Metrology has to be an isolated hardware block in some countries, it is the regulations, plus injecting high currents for PLC from the chip makes it difficult to keep noise down for class 05 meters and Class 01 meters,” said Teijeiro, “We are working to have a metrology chip very soon, I am not saying when.”
And a display driver?
“There is no display driver because the trend in market is to have chip-on-glass displays,” said Teijeiro. “If you have a display driver, you have to have a lot of space on PCB as there are lots of pins, and you create EMI. We just have an interface for the display.”
With the transmitter off, power consumption is 200µA/MHz and 30µA in wait mode. Receive sensitivity is up to 34.8dBµV and dynamic range is up to -73.18dB.
The embedded PRIME-compliant software stack is available free.