Analog Devices

Adc Driver Amplifier

Harmonic distortion products are higher in frequency than the frequency of interest, so their amplitude may be reduced by system band-limiting. The internal common-mode feedback loop produces outputs that are highly balanced over a wide frequency range without requiring tightly matched external components.

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As A s rolls off, loop gain decreases and distortion increases. The driver outputs can stay away from the supply rails, allowing decreased distortion. However, it is important to note that amplifier gain equations are based on the assumption of a zero-impedance input source.

Phase margin and stability increase as R F increases, and decrease as R F decreases. Your existing password has not been changed. Resend Verification Email. Electronic noise is integrated over a bandwidth that includes the frequency of the last harmonic to be considered.

For small gains, the change in input resistance is small and will be neglected for the moment, but the feedback factors must still be matched. Interestingly, the gain in the gain-bandwidth product is the reciprocal of the averages of the two feedback factors. Systems running on dual supplies, with single-ended or differential inputs and ac- or dc-coupling, are usually fine with either type of input stage because of the increased headroom.

Thank you for verifiying your email address. More information about text formats. So, look to the data sheet graphs of harmonic distortion to make your decision. This point can be easily located on the open-loop transimpedance and phase plot, in the same way as for the voltage-feedback amplifier. Parasitic capacitance is especially dangerous at the summing nodes of an amplifier, by introducing a pole in the feedback response, causing peaking and instability.

This is not the case for single-ended drivers, however. The approach using a single differential driver is simpler than the multi-amplifier approach, and the specialfunction level translation driver approach is simpler yet.

ADC Drivers

Also make sure there is ground plane under long traces to minimize trace inductance. We didn't recognize that password reset code. The considerations differ between input and output coupling. Optimum performance is achieved when a transmission line is terminated at both ends in its characteristic impedance. The role of power-supply pins as inputs to the amplifier is often ignored.

Driver Amplifiers For Analog-To-Digital Converters

An excellent way to determine the usable bandwidth is to consult the distortion plots on the data sheet. Lines and paragraphs break automatically. For the discussions that follow, some definitions are in order. Of particular concern are load capacitance, feedback loop inductance, and summing-node capacitance. Consider the sine wave output at the slew rate.

Current-feedback amplifiers should always use purely resistive feedback with sufficient phase margin. The key specification is phase margin. With unmatched feedback factors, the effective feedback factor is simply the average of the two feedback factors. The need for it will become apparent in the following example. We've sent you an email with instructions to create a new password.

Rules of the Road for High-Speed Differential ADC Drivers

As the output voltage of the driver approaches the rail, intel 855gm video chipset driver the amplifier loses linearity and introduces distortion. Why would I want to use an active driver instead of a passive transformer?

They also exhibit lower distortion and faster settling time than singleended drivers. Overcoming common challenges driving an amplifier with a photodiode.

Important in most applications, noise is usually the most important performance metric in broadband systems. It would be contradicting to be using a system that is lacking of performance. Minimizing undesired parasitic reactances starts with keeping all traces as short as possible. Also, using multiple bypass capacitors on the power supplies will help ensure that a low impedance path is provided for broadband noise. Use of ground plane, and grounding in general, is a detailed and complex subject and beyond the scope of this article.

In a real current-feedback amplifier, loop gain does have some dependence on closed-loop gain, but not nearly to the extent that it does in a voltage-feedback amplifier. The loop gain of an ideal current-feedback amplifier does not depend upon a closed-loop voltage gain, so harmonic distortion performance does not degrade as closed-loop gain is increased.

Each of these parasitic reactances adds lagging phase shift to the feedback loops, thereby reducing phase margin. That provides a rough figure for comparing amplifiers. Nevertheless, within the first or second Nyquist zone, a transformer or an amplifier can be used. Two differences from a traditional op-amp feedback circuit can be seen.

Low harmonic distortion in the frequency domain is important in both narrow-band and broadband systems. This is a starting point for calculating the termination resistance.

Specialized amplifiers may provide level shifting, interstage isolation, single-ended to differential conversion, differential to single-ended conversion, plus attenuation or gain. Likely I'd screw up everything because my calculations have screwed up somewhere! Parasitic elements rob high-speed circuits of performance. With voltage-feedback amplifiers, it is best to use the smallest possible R F in order to minimize the phase shift due to the pole formed by R F and the summing-node capacitance.

ADC Drivers

We've sent an email with instructions to create a new password. Still looking at frequency response, some amplifiers provide dc coupling. The simplest way to accomplish this is to add resistance to the lower R G. Happy to call in other professionals to test my system for me too as long as I don't have to try and work it all out on my own! If a more-exact overall gain were necessary, higher precision or series trim resistors could be used.

Driver Amplifiers For Analog-To-Digital Converters

The gain-bandwidth product of the voltage-feedback architecture is constant. In fast-throughput devices, the acquisition can be as low as a few dozen nanoseconds. For basic amplifier applications, the feedback is purely resistive, introducing no phase shifts around the feedback loop. Create New Password We'll send you a link to create a new password. This common-mode definition is intuitive when applied to balanced inputs, but it is also valid for single-ended inputs.

Adc driver amplifier

ADC Drivers

Several iterations are required for these cases. Drivers with shifted input common-mode ranges generally work best in dc-coupled systems operating on single supplies. Most people are not familiar with electromechanical spinning.

ADC Drivers