Analog Top Talks in September 2019 on EDABoard.com

Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around analog ICs and analog design. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com.

12V DC vending machine motor – I have made some changes with a motor to work with the micro limit switch. But the problem is sometimes the motor rotates 1 full 360 degree rotation which is perfectly fine but sometimes the motor rotates 2 full or 1 and half rotation which is wrong. I do not know the reason. Read more

A look at a linear amplifier – I want to develop a 3-phase-calibrator. My application needs to amplify the signal to a certain level. Class D switching is necessary. Read more

Problem in plotting I/O waveform  – I want to plot the I/O characteristics of PFD to see the dead zone. Can anyone please elaborate on the process of how to sweep the variable? Read more

Transimpedance amp for DC only –  I’m using a classic TIA configuration to measure leakage current through coax insulation in the 200nA range. The circuit works well using a V source and resistor to calibrate but when I connect the long, high capacitance cable the noise is terrible. Can I bandwidth limit the op amp to say 1-2Hz using a large capacitance across Rf (1 Megohm) or am I having issues due to a large cap (>10,000pF) at input? Read more

TRIAC won’t conduct – I am having a problem with the Triac conducting. In the attached schematics, the Triac should control current through R1 by turning potentiometer. I am well aware of the position of pins regarded to the gate terminal. At first, I thought that maybe I have switched pins but that is probably not the case. Read more

 

Antenna PCB in commercial key fob – Can anyone tell me what kind of antenna in some key fob. From what I can see, it is just a trace that is 7.5 cm length (the frequency 315 MHz). Read more

Variable gain amplifier – We need a very simple, variable gain amplifier. We have a half-sine control voltage which we wish to gradually vary the magnitude of (i.e. not different discrete switchable gain levels). Read more

Active precision current limiting circuit – I’m trying to design a precision active current limiter circuit to limit output current down to 100mA. I saw many different circuits in net, some made by BJT transistors which are not precision enough. I don’t have much space on my PCB, so the priority of the design is to be simple and small-sized. Do you have any suggestions for compact ICs to limit the desired current value by a setting resistor only? Read more

S parameter extraction for MOSFET internal parameters – In this book Radio Frequency Integrated Circuit Design Second Edition, John W. M. Rogers Calvin Plett mentions the equation for MOSFET internal capacitors, resistors and gm. How accurate are these values because the values I get from DC operation point (from Spectre) are so different from these equations. Read more