Electronic amplifiers have been around for over 100 years, first as vacuum tubes then, starting in the 1940s, using transistors. In the 1960s researchers learned how to miniaturize and place dozens of transistors into packages no bigger than a nickel. When configured in a certain way these transistors make what is called an Operational Amplifier, or Op Amp. (I wrote a history of the Op Amp in a previous blog titled Beyond the Tilted Triangle.)
Two of the most important qualities of an op amp are Signal to Noise ratio and Distortion. Don’t worry, I promise – no math.
Let’s start with Signal to Noise, which engineers shorten to SNR. Since every amplifier has an input and an output, users of the amp need to know how much detail from the original, input signal they can expect at the amplified output. The challenge for op amp designers, especially for those amps intended for industry, test equipment, and healthcare devices, comes from the fact that the places where those devices are located are very noisy places. Further, the signals going into the amplifier, like from a blood flow monitor or a sensor in a factory, are usually very small. Only an op amp with a high SNR can amplify and reproduce the signal accurately by extracting the intended signal from the extraneous surrounding noise.
Distortion tells the user about the quality of the signal through the amp. An analogy is the children’s game in which a child passes along a message by whispering into the ear of the next child in a line or circle (we called it Telephone where I grew up, but some folks called it Whispers). Laughter inevitably ensues when the final child in line says out loud the message they heard from the next-to-last participant. (I distinctly remember a line of twenty kids in elementary school turning “Four score and seven years ago” into “My aunt hates apple pie.”) An amplifier that distorts the original signal is of no use to anyone – I certainly wouldn’t want a piece of equipment in my doctor’s office to have an amplifier that distorts my data. What designers of sensitive equipment require are transparent amplifiers, meaning the amplifier has done its job without changing the signal. This is critical, especially when the amplified signal is going to be converted into digital data so it can be analyzed. It must be an accurate reproduction or else the result is useless.
Let’s talk a bit more about the job converting signals into digital. No doubt you have heard people say, “life is a compromise.” I’m not going to argue the point, only to say it goes double for engineering. Designers are often faced with a compromise between speed (how fast the amplifier can respond to changes in the incoming signal) and resolution (how much detail of the original signal the amplifier passes to the converter) especially in the presence of system and environmental variations like battery voltage and temperature. Analog Devices new op amp, known as the LTC6228, addresses the speed vs. resolution challenge with an architecture reducing the traditional trade-offs faced by product designers. With the signal flexibility found in the LTC6228, designers no longer have to design in an amplifier simply because it is compatible with either the sensor on its input or the converter on its output.
Details on the LTC6228 can be found on its product page here. There is also a version in which there are two of these fast, low distortion amplifiers in one chip, the LTC6229. Both the single and dual versions come in five different package types and sizes – some ultra-small – so designers can save space on their board for more features. ADI’s new LTC6228 and LTC6229 offer the performance, robustness, and versatility designers have been seeking.