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All of the ADCs I found online have an input range on the order of few volts, e.g. 0 to 5 or -4 to +4. But my signal is in the mV range. Are there any ADCs with such a small input range? I know I can add an op amp but if I can avoid that it will be better.

Edit: required resolution is 16 bits, sampling rate is 300 ksps.

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    \$\begingroup\$ I doubt it. You want to amplify it anyways to make it more immune to noise on its way to and inside the ADC. \$\endgroup\$
    – DKNguyen
    Oct 14, 2019 at 22:07
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    \$\begingroup\$ Amplification will increase the effective resolution of the ADC. Without amplification, a signal "in the mV range" will only give you two or three bits of resolution with typical ADCs. \$\endgroup\$ Oct 14, 2019 at 22:13
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    \$\begingroup\$ @student1 The noise at the signal source is not the only noise that will always be in the signal. Just because there are no rats in the wheat when it leaves the farm doesn't mean there won't be rats in the wheat by the time it gets to the mill. \$\endgroup\$
    – DKNguyen
    Oct 14, 2019 at 22:31
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    \$\begingroup\$ It is extremely difficult (read expensive) to make an ADC with microvolt resolution - it is much more cost-effective to make the ADC with inputs in the volt range and amplify the signal externally to the level required by the ADC. The amplifying device does not have to make the compromises that would be required if it was implemented within the ADC device so it can have a lower noise level. \$\endgroup\$ Oct 14, 2019 at 22:56
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    \$\begingroup\$ @analogsystemsrf Using dB for DC gain is painful. Not wrong, just painful. \$\endgroup\$ Oct 15, 2019 at 2:50

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You really did not tell us anything about the ADC specs that you require. Various manufacturers like Analog Devices and TI have vast lines of products, including integrated parts that have PGA (programmable gain amplifier) front ends.

Here is a copy and paste from A TI webpage with a full scale input range in hundreds of millivolts.

"The ADS111x perform conversions at data rates up to 860 samples per second (SPS). The PGA offers input ranges from ±256 mV to ±6.144 V, allowing precise large- and small-signal measurements. The ADS1115 features an input multiplexer (MUX) that allows two differential or four single-ended input measurements. Use the digital comparator in the ADS1114 and ADS1115 for under- and overvoltage detection."

Don't give up yet. Keep searching. There are tons of devices out there.

Linear Technology was bought out by Analog Devices so it has a huge product line.

TI has been buying companies for years like Burr Brown and National Semiconductor so it;s product line is extremely large as well.

Here is the link for the TI product; TI ADC

Again, you did not mention what, speed, resolution, etc. that you need so the above example may or may not be of interest to you.

Hope this helps a bit .....

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