3.4.8 Metrology

The Energy Metering Analog Front End peripheral (EMAFE) of SAM4CMS16C embeds four high-resolution Sigma-Delta Analog-to-Digital Converters followed by SINC decimation filters running at an output data rate of 16kS/s. The two current measurement channels feature a low noise programmable gain amplifier to accommodate any type of current sensor configured in any type of IEC/ANSI-C application. One of these channels is dedicated to neutral current measurement to implement anti-tamper functions.

The EMAFE also embeds a high-performance voltage reference and a die temperature sensor. The temperature characteristics of these functions are measured during manufacturing and stored in an internal read-only memory. A low-cost and efficient voltage reference temperature correction can then be implemented at the software level. The EMAFE has three types of acquisition channels:

• Voltage channel
• Current channels
• Tamper and temperature channels

All these channels are built around the same Sigma-Delta A/D converter. The voltage reference of this converter is the VREF_AFE pin voltage referred to ground (GND pin). This reference voltage (with a typical output voltage of 1.144V) can be internally or externally sourced. The converter’s sampling rate is EMAFE_CLK/4, typically 1.024 MHz. An external low-pass filter, typically a passive R-C network, is required at each ADC input to reject frequency images around this sampling frequency (anti-alias).