Active Feedback Amplifier Enables High-Performance A-To-D Conversion

April 2, 2001
Designers employing high-performance analog-to-digital converters (ADCs) have a common problem: there are few, if any, amplifiers on the market that can provide the accuracy needed to buffer an input signal and drive a 16-bit ADC without a loss of...

Designers employing high-performance analog-to-digital converters (ADCs) have a common problem: there are few, if any, amplifiers on the market that can provide the accuracy needed to buffer an input signal and drive a 16-bit ADC without a loss of performance. A 10-V full-scale ADC must be able to resolve 150 µV. This is a tall order, even when the input frequencies are as low as 100 kHz.

To compound the matter, many of today's ADCs have a full-scale range of 5 V. Any buffer used to drive such a device must contribute no more than 75 µV of error or the system performance will be compromised. This low-noise and low-distortion requirement ensures that a finite-bandwidth amplifier (e.g., fT = 30 MHz) is simply incapable of such performance.

Total error = root-sum-squared (noise, distortion, CMRR, gain error) < 75 µV

This device improves state-of-the-art circuitry by about 20 dB over currently available buffers (Fig. 1). Two amplifiers make up the system. The second amplifier is contained in the feedback loop of the first amplifier and configured for a gain of one.

Note that VOUT is approximately equal to VIN. The voltage at TP2 is similar to VIN as well. Consequently, the error be-tween the noninverting terminals and inverting terminals of the first amplifier is the same as the error between the noninverting and the inverting terminals of the second amplifier. Therefore:

VOUT = VIN + VERROR1 − VERROR2

or

VOUT = VIN

Figure 2 shows the performance of this circuit for a 0- to 2.5-V sinewave input at 10 kHz. When comparing the error (VOUT − VIN) in the bottom trace to that of the buffer alone (VOUT − VTP2) in the middle trace, a significant error reduction can be observed. Figure 3 shows a similar improvement for a ±10-V triangle waveform input at 1 kHz. The amplifier bandwidth was programmed to be 30 MHz.

Sponsored Recommendations

Board-Mount DC/DC Converters in Medical Applications

March 27, 2024
AC/DC or board-mount DC/DC converters provide power for medical devices. This article explains why isolation might be needed and which safety standards apply.

Use Rugged Multiband Antennas to Solve the Mobile Connectivity Challenge

March 27, 2024
Selecting and using antennas for mobile applications requires attention to electrical, mechanical, and environmental characteristics: TE modules can help.

Out-of-the-box Cellular and Wi-Fi connectivity with AWS IoT ExpressLink

March 27, 2024
This demo shows how to enroll LTE-M and Wi-Fi evaluation boards with AWS IoT Core, set up a Connected Health Solution as well as AWS AT commands and AWS IoT ExpressLink security...

How to Quickly Leverage Bluetooth AoA and AoD for Indoor Logistics Tracking

March 27, 2024
Real-time asset tracking is an important aspect of Industry 4.0. Various technologies are available for deploying Real-Time Location.

Comments

To join the conversation, and become an exclusive member of Electronic Design, create an account today!