# How to find the dynamic range of ADC?

I bought a Analog to Digital Converter but did not gave much attention to Dynamic range. The resolution is 12 Bit. Minimum input voltage is 0V and maximum is 5V.

The problem is I don't have the datasheet and want to know how can I find the Dynamic range of this ADC?

Additional info: It says it has 10Megasample per sec of sample-rate.

• Given the part number you can easily find the datasheet, which will answer the question. – Brian Drummond Jul 10 '14 at 11:05
• Did you mean 'I have a homework question that noone wants to answer so I try it this way'? electronics.stackexchange.com/questions/118457/… – RJR Jul 10 '14 at 12:54

The dynamic range is the ratio of the maximum voltage to the minimum voltage that the ADC can convert. The maximum voltage is 5 volts. Since it is a 12 bit converter, it has a resolution of 212 - 1 or 4095. Thus the minimum voltage, for which the ADC would have only the least significant bit set, is 1.22 millivolts. So the dynamic range of your ADC is 5/.00122 = 4095 = 72.2 dB. In general, the dynamic range is only a function of the number of bits, not the maximum input voltage. But I calculated using voltage just to show you the details.

• That provides an upper limit on the dynamic range. The true figure will be lower, and depend on the actual device and the circuitry around it. – Brian Drummond Jul 10 '14 at 11:31
• I thought that the resolution would be 1.22mV and the dynamic range is analogous to the input range - 5V. The wiki says "[Dynamic Range is] .. the ratio between the largest and smallest possible values of a changeable quantity". – sherrellbc Jul 10 '14 at 12:34
• @Barry you said it has a resolution of 2¹²-1 or 4095 but according to the wiki en.wikipedia.org/wiki/Analog-to-digital_converter it is just 2¹²? – Lifestohack Jan 7 '15 at 7:57

The dynamic range is the ratio (usually expressed in dB) between the noise floor of the ADC and the maximum input.

As Brian says in his comment, the quantization noise sets a lower limit on the noise floor at the actual sample rate, however the noise of a real ADC will be higher than the quantization noise.

Also, if you take your 10Msps ADC and band-limit and decimate the output to a lower sample rate the dynamic range can be increased, by as much as 10dB for a decade of down-sampling.

• What do you mean by quantization noise and noise of the ADC? I understand what quantization is, but not its use in the context of noise. Do you mean that the dynamic range of the ADC will be impacted due to the quantization of noise superimposed on the signal we are attempting to digitize? (i.e. signal to sample + noise floor?) – sherrellbc Jul 10 '14 at 12:54
• @sherrellbc There will be some internal noise in addition to the quantization noise. The effective number of bits (ENOB) of a "24-bit" ADC might be 19 bits under certain conditions, so if you use 24 bits in the calculation you'll be overly optimistic. – Spehro Pefhany Jul 10 '14 at 12:59
• I see - similar to calculating significant digits beyond the precision you know certain variables to. How much you determien the ENOF of a particular ADC? Experimentation with high-precision voltages? How exactly would you define "quantization noise"? I find very little when searching that term. From what I gather the definition seems to parallel quantization error, but are they exactly the same thing? – sherrellbc Jul 10 '14 at 13:22
• @sherrellbc ENOB is often listed in the datasheet. It's always less than the actual number of bits (because quantization noise sets a lower floor). – Spehro Pefhany Jul 10 '14 at 13:24

THE dynamic range of your ADC is calculated as DR= 6.021*N + 1.763 dB where N= is the number of bits i.e 12 bit DR= 74dB.

• Can you explain the constant 1.763dB here? I can understand that each new bit doubles the voltage range, so provides ~6dB of dynamic range, but not sure how a 0 bit ADC would have 1.763dB of dynamic range ;) – Wayne Uroda May 26 '17 at 5:27
• I found a link to a very in depth derivation here: analog.com/media/en/training-seminars/tutorials/MT-229.pdf – Wayne Uroda May 28 '17 at 12:47