Hi,
I have gone through the previous posts regarding microvolt measurement , such as (https://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/293906
Hello Tyagi-san,
For a moment, consider how small a 1 uV signal is relative to the noise generated internal to a circuit and that normally encountered in practical circuits. If you are considering an application that is broadband and has a 1 MHz bandwidth that is one consideration, but if the application is a very narrow bandwidth amplifier centered on 1 MHz that is another. An op amp circuit is usually a broadband amplifier unless it is set up as a filter; while the latter narrowband circuit is more likely satisfied with a low-noise discrete amplifier circuit.
When I consider using one of our low-noise precision amplifiers having gain-bandwidths below 50 MHz in a broadband amplifier applications, they are already in the frequency roll-off region at 1 MHz. The total output noise generated by the op amp and the resistors for gain of 100 V/V is in the hundreds of microvolts. Although a 1 uV input signal would be amplified by the same 100 V/V gain, its amplitude relative to the noise amplitude would not be significant. The net result is the desired 1uV signal would have a substantial amount of noise modulating it. Just how much would depend on the noise characteristics of the paricular op amp and the resistors selected.
There are low noise, wideband op amps that might provide acceptable levels of performance. These are in the catagory that TI specifies as High-Speed Amplifiers. An example of one of these amplifiers is the THS4032. You can find its datasheet here:
The High-Speed Amplifiers are supported by another TI op amp group and they have their own E2E forum. They may be able to assist you with information about the practicality of amplifying a 1 MHz, 1 uV signal using high-speed op amps. Any approach you take will require cascading multiple amplifier stages to bring the 1 uV signal up to a usable amplitude.
A 1 MHz, 1 uV signal is essentially an RF signal, similar in amplitude to radio signals. Try doing a web search for low-noise, RF amplifiers that are optimized for the 1 MHz frequency range. Discrete transistor amplifiers for RF applications usually have very low noise figures. You might want to consider a design consisiting of a discrete, low-noise pre-amp stage, followed by high-speed op amp stages.
Regards, Thomas
Precision Amplifiers Applications Engineering
