Constantin
Well-known member
So one of the ADCs I've been using is a MCP3911, which microchip calls an analog front end, which is specialized for power measurements. One of the interesting aspects of this device is that it advertises 24bit resolution with no missing codes yet, the the highest effective number of bits is about 16 per the data sheet (depends on how you use it). Per Wikipedia, "ENOB specifies the resolution of an ideal ADC circuit that would have the same resolution as the circuit under consideration". My interpretation is that if you manage everything right re: the PCB, layout, components, etc., that the best you will be able to do with this ADC is 16 bits.
The MCP3911 communicates via SPI and the Voltage and Current readings are transferred in 8 bit increments. Thus, the device offers 3x8bit transfers per power register to read out a 24-bit number or a truncated/rounded/etc/ 16-bit number via 2-8bit transfers. It seems weird that a manufacturer would promote downloading 24-bit data packets for a ADC that at best can achieve 16 ENOB.
Why would one even offer 24-bit readouts if the ADC can't be relied on to produce accurate data at that resolution? (at least if I understand the meaning of ENOB). For the follow-on device (MCP3910) they even offer 32-bit register readouts so you can get a signed 24-bit value. Seems like a fools errand to me, or am I missing something?
The MCP3911 communicates via SPI and the Voltage and Current readings are transferred in 8 bit increments. Thus, the device offers 3x8bit transfers per power register to read out a 24-bit number or a truncated/rounded/etc/ 16-bit number via 2-8bit transfers. It seems weird that a manufacturer would promote downloading 24-bit data packets for a ADC that at best can achieve 16 ENOB.
Why would one even offer 24-bit readouts if the ADC can't be relied on to produce accurate data at that resolution? (at least if I understand the meaning of ENOB). For the follow-on device (MCP3910) they even offer 32-bit register readouts so you can get a signed 24-bit value. Seems like a fools errand to me, or am I missing something?