Active analog filters can be found in almost every electronic circuit. Audio systems use filters for frequency-band limiting and equalization. Designers of communication systems use filters for tuning specific frequencies and eliminating others. To attenuate high-frequency signals, every data acquisition system has either an anti-aliasing (low-pass) filter before the analog-to-digital converter (ADC) or an anti-imaging (low-pass) filter after the digital-to-analog converter (DAC). This analog filtering can also remove higher-frequency noise superimposed on the signal before it reaches the ADC or after it leaves the DAC. If an input signal to an ADC is beyond half of the converter’s sampling frequency, the magnitude of that signal is converted reliably; but the frequency is modified as it aliases back into the digital output.
Designing active analog filters in minutes - [Link]
All about opamp input bias currents. Dave goes through the theory, and then does some practical measurements and tweaking.
Opamp Input Bias Current - [Link]
Designing and measuring basic and precision opamp peak detector circuits.
Peak Detector Circuit - [Link]
Bruce Trump writes:
Slewing behavior of op amps is often misunderstood. It’s a meaty topic so let’s sort it out.
The input circuitry of an op amp circuit generally has a very small voltage between the inputs—ideally zero, right? But a sudden change in the input signal temporarily drives the feedback loop out of balance creating a differential error voltage between the op amp inputs. This causes the output to race off to correct the error. The larger the error, the faster it goes… that is until the differential input voltage is large enough to drive the op amp into slewing.
Slew Rate – the op amp speed limit - [Link]
Have you ever wanted to take a standard voltage op-amp and turn it into a high voltage output circuit? Here is a technique that requires some shunt regulators to power the chip and some current limiting transistor circuitry for the output. This example should work upto +/- 120V.
Make an Op-Amp High-Voltage Output Circuit - [Link]
This is a great video of Alan Wolke talking about op-amp power supply options. He explains the differences when using op-amps on a single supply, a split (or bipolar) supply and virtual ground.
This video discusses the power supply considerations for op amps. It talks about split or dual power supply and single supply operation, and why the op amp often doesn’t care which you use! It shows how traditional op amps designed for split supply operation can be used in single supply applications. The most important consideration generally is taking care of where the input and output voltages are with respect to the supply rails. The input voltage and output voltage range specifications are examined in a datasheet. The operation of a op amp in a single supply application is examined on an oscilloscope. This operation is compared to a modern rail-to-rail op amp in the same circuit.
Op Amp Power Supplies: Split, Single, and Virtual Ground Designs - [Link]
Kerry Wong shows how to make an adapter circuit for measuring very low voltages with a multimeter.
A typical 3 ½ or 4 ½ multimeter can measure voltage in the low mV range and current in the low mA range. Voltage measurement in the µV range and current measurement in the nA range are typically only available in the more expensive lab bench multimeters. In this post, I will show you a simple adapter circuit that can be used for precision voltage measurement down to the µV range. Using this circuit along with the current adapter circuit I discussed earlier you will be able to perform most of the low level measurements with a 3 ½ meter.
Precision Voltage Adapter For Low Voltage Measurement - [Link]
The MAX44281 is the industry’s first op amp in a 4-bump WLP package, designed for use in portable consumer and medical applications. This device is offered as a noninverting amplifier with gain (AV) of +1V/V, +2V/V, or +10V/V. The device features rail-to-rail output, low 100µV input voltage offset, and 15MHz of bandwidth with only 700µA of supply current. The device is available in an ultra-small, 0.86mm x 0.86mm, 4-bump WLP package with 0.5mm height.
MAX44281 – Ultra-Small, Ultra-Thin, 4-Bump Op Amp - [Link]
The LTC6090 is a high voltage precision operational amplifier. The low noise, low bias current input stage is ideal for high gain configurations. The LTC6090 has low input offset voltage, a rail-to-rail output stage, and can be run from a single 140V or split ±70V supplies.
The LTC6090 is internally protected against overtemperature conditions. A thermal warning output, TFLAG, goes active when the die temperature approaches 150°C. The output stage can be turned off with the output disable pin OD. By tying the OD pin to the thermal warning output, the part will disable the output stage when it is out of the safe operating area. These pins easily interface to any logic family.
The LTC6090 is available in an 8-lead SO and 16-lead TSSOP with exposed pad for low thermal resistance.
LTC6090 – 140V CMOS Rail-to-Rail Output, Picoamp Input Current Op Amp - [Link]
Gerard Fonte writes:
My client, a small manufacturer, was having a noise problem with a new batch of 1500V-dc supplies.
It had been a while since the company manufactured this product. The original engineer was long gone, and the only documentation was a schematic. The approach was a straightforward closed-loop design. An op amp controlled an oscillator that used a step-up transformer to create the high voltage, which the system rectified and filtered into dc. A small part of the output voltage fed back into the inverting input of the op amp as an error signal to adjust the oscillator frequency when necessary. The noninverting input was grounded.
Tracing down a noise problem – an interesting story - [Link]