Monitoring the voltage level of a coin cell in a portable device or in back-up service is a common, simple application for modern CMOS operation amplifiers (op amps).
Figure 1 shows an implementation using the 1.8-V, OPA333 zero-drift op amp. The coin cell has a voltage of 3 V, while the circuit is powered by a 3- to 5-V level.
Oddly, I’ve had customers report that the circuit drains the coin cell long before the expected…
Tim Green
Here is the moment you have all been waiting for – the answers to the six op amp puzzles I posted last week. You know, the ones that you have all been puzzling and puzzling until your puzzler is sore! Score your number of right answers and bestow upon yourself the appropriate ranking at the end of this blog!
Repeated for reference are some key op amp specifications in Figure 1. By the way, the specifications…
In honor of National Puzzle day here in the United States of America, I humbly present six op amp puzzles for you to puzzle on until your puzzler is sore – or at least until next week when I will publish the right answers!
I’ve even provided you with some key op amp specifications to help in Figure 1.
|
PARAMETER |
|
CONDITION |
UNIT |
|||
|
MIN |
TYP |
MAX |
||||
|
|
|
Vs=±5V unless otherwise… | ||||
Package level trim is a semiconductor manufacturing method that achieves highly accurate amplifiers and other linear circuits. The key measurement of accuracy for an amplifier is its input offset voltage. The input offset voltage is an error voltage at the input of the amplifier measured in microvolts. This error voltage can range from tens of microvolts to thousands of microvolts.
Amplifiers and other semiconductor…
Engineers have struggled for decades to understand the mysterious plot of common-mode voltage (VCM) vs. output voltage (VOUT). The most common VCM vs. VOUT shape appears in Figure 1, although the shape often varies by device and setup configuration.
As VCM approaches the supplies, the input/output limitations of the internal op amps restrict the VOUT range of the device. Therefore, the output swing for an applied VC…
Winter is my favorite time to work on hobby projects in Texas. My garden is filled with easy-to-maintain winter or cover crops, and it’s cool enough to work outside without overheating.
While working on a recent project, I had to re-route some electronic wiring away from an off-road vehicle’s alternator because capacitive coupling was introducing noise from the alternator into the wiring. The project reminded me…
In my last blog post, I discussed why instrumentation amplifier power supply rejection ratio (PSRR) and common mode rejection ratio (CMRR) improve as the amplifier’s gain increases.
Returning to the simplified model of an instrumentation amplifier shown in Figure 1, we recall that PSRR and CMRR are input referred specifications.
Figure 1: A conceptual model of an instrumentation amplifier
In higher gains…
Electrical engineers are accustomed to dealing with rejection, and we absolutely love it. From common-mode rejection to power supply rejection, and even EMI rejection. The more rejection, the better!
However, in the case of instrumentation amplifiers, it’s easy to get confused when calculating the offset shift caused by a change in the power supply or common-mode voltage. The root…
Power supply rejection ratio (PSRR) describes how well an operational amplifier (op amp) rejects variations in power supply voltage. PSRR is defined as the shift in offset per volt of shift in power supply, and generally is given units of micro-volts per volt (uV/V).
The OPA209, for example, has a typical PSRR of 0.05uV/V. Thus, for the OPA209, the power supply can…
Last week for Halloween, I handed out candy to kids in all sorts of costumes. Some occupations make great costumes: fireman, policeman, doctor, professional athlete, and of course astronaut. But I’ll admit that every year I’m a bit disappointed that no little electrical engineers come to the door.
Sure, some of you may say things like, “it’s dangerous to let a child walk around the neighborhood with a soldering…
In this month’s post on our sister blog, the “Precision Hub” on Planet Analog, I share a recent question I got from a customer in the Precision Amplifier Forum here in the TI E2E™ Community.
His circuit used an op amp to amplify the output of a microphone at very low frequencies. He used a large (47uF) AC coupling capacitor and a high input resistance (100kΩ) to achieve a low corner frequency for…
When troubleshooting non-functional or poorly performing circuits, engineers often run simulations or other analyses that consider the circuit at the schematic level. If these methods fail to resolve the issue, even the best engineer might be left feeling stumped, frustrated, or confused. I’ve felt this pain myself. To prevent you from reaching a similar dead end, I present to you…
This technical article was updated on July 23, 2020.
Engineers like to simplify the design process using many rules to get the design going in the right direction before optimizations occur. One of my favorites is to always drive the inputs of an analog-to-digital converter (ADC) with a low impedance source. Why do I like this one so much? Because it offers many benefits for a precision data acquisition block.
Let’s start…
In this month’s post on our companion blog, the “Precision Hub” on Planet Analog, I share an idea I had about EMI and lightning.
After watching a storm, I started thinking about the EMI challenges we encounter with precision systems. I wondered if I could use EMI to my advantage to detect lightning during a thunderstorm. So, I built a lightning detector to see what would happen.
Check out my full post…
This technical article was updated on July 23, 2020.
Last week, I replaced the carpet in my house with wooden flooring. After removing the carpet from the staircase in our living room, I noticed my “uniform” staircase actually had very uneven steps. This was a surprise to me, because in all the years I walked up and down the same staircase, I had never noticed this unevenness. The…
Thermal noise in analog design is almost always parasitic and should be avoided at all costs. Input filtering, PCB layout and grounding are paramount to good analog system designs, but you’ll always find some amount of thermal Johnson-Nyquist and flicker noise in an analog system.
An additional noise source, quantization noise, can actually outweigh the noise from thermal and…
Before working as an applications engineer, I worked as an IC test development engineer here at TI. One of my projects was to characterize an I2C temperature sensor. After writing some software, I threw together a hand-wired prototype board. I was in a hurry, so I left off that pesky decoupling capacitor. Who needs it, right?
I collected data for about a week, and none of my results matched expectations. I made numerous…
Our monthly post on our sister blog, the “Precision Hub” on Planet Analog, focuses on transient stability testing.
In it, I share a recent experience I had with one of our summer interns. He was taking transient stability data on a design and learned an important lesson – the step size of the output signal is extremely important to achieve accurate results.
Read my full post, "Transient stability…
In the last few months, I’ve seen at least four cases of the wrong understanding of the “real Vos” of an op amp.
Figure 1 shows the specs for the OPA363 op amp, a single supply 1.8V to 5.5V op amp with 7MHz of unity gain bandwidth and a 5V/us slew rate. I’ve put a box around the real Vos of the OPA363 in the table below.
NOT! The real Vos of the OPA363 is directly…
“A clever person solves a problem. A wise person avoids it.” – Albert Einstein
Albert Einstein would have loved analog design – there is always an element of relativity involved. For example, in data acquisition systems, accuracy is relative to your data converter’s reference voltage.
It’s up to the wisdom and foresight of the designer to evaluate the necessary tradeoffs to achieve optimal…
As an applications engineer, I field a lot of questions from system designers on how to decipher datasheet specifications. Just when I think I understand how specifications are determined and how they translate to error in a design, I’ll get a TI E2E™ Support Forum post, phone call or e-mail from a customer that shows otherwise.
I actually got a question the other…
It’s been three weeks since we launched “The Hub” here on E2E, and we’re already branching off into new and exciting areas. Today we kicked off a sister blog on Planet Analog called the “Precision Hub” with a blog post from me on direct current sensing.
In the post, I answer a question I get a lot from customers – what do you do when you want to measure three decades of load current…
As we get ready to "gear up” here on the TI Precision Designs Hub (AKA "The Hub), we thought you might want to first learn a little about the experts who will be sharing their analog design tips with you in the coming weeks and months.
They’ve each provided a favorite tip to keep in mind when designing with analog, along with a brief overview of their analog experience.
Can you match the blogger…
hub (hub)
noun
1. the central part of a wheel, into which spokes are inserted.
2. a center around which other things revolve or from which they radiate.
Welcome to the TI Precision Designs Hub. Our new home here on E2E to provide tips, tricks, and design techniques for board- and system- level designers brought to you by the authors of TI Precision Designs – our new precision analog reference design library.
We chose…
