Analog Top Talks in September on EDABoard.com forums

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.

Load seen by opamp in non-inverting config – I’ve come across the result that the load seen by an opamp is radically different depending if it’s in inverting or non-inverting configuration. I wonder if I’m making some mistake, or if it’s a well-known fact and I was just ignorant. Read more

Using MOSFET to turn on/off auxiliary electronic circuit – I have custom-build e-bike which is basically a motor, battery, controller and an LCD screen with 3 buttons. When I push ignition button, the LCD sets voltage on one of its signal wires (blue) to 51 – 67.2V (BAT+, depending on battery capacity) which is then wired to the controller. I would like to sense voltage on this ignition wire and switch on/off an external dc-dc converter (8-72V to 5V5A) in order to charge my phone while riding a bike. Read more

Ear headphone with low sound – i want to amplifi audio signal from phone. i have ear headphone with low sound
to do that I want to use smd dual op amp . 1/2 for right the rest for left
vin =0.7v , power in= 1mw
gain=3
power source : 2 coin cell 3v
speaker = 600 ohm (from some set)
could it work without lead from op amp to another
and is there any error. Read more

 

How to reduce input referred noise of an amplifier – I want to reduce input referred noise of an op-amp more specifically of an OTA. OTA is to be designed for low-frequency filter. For low frequency as fc = gm/CL, therefore for low frequency I need low gm value. Due to this small gm my noise is very high around 900uV/sqrtHz. How can I reduce this input referred noise. Read more

Detection of power failure for ups – I am trying to build a line interactive ups, using Arduino as the brain, and at a stage of building the sensors, this one is getting bit complicated, the mains voltage measurement, so I have a bridge rectifier 6v step down, with voltage divider along with a capacitor, 10k-4.7k divider with 47uf cap. this is actually taken from the sine wave inverter circuit using 16f72 that was I think a commercial inverter. Measuring the voltages has been fine. but the time constant in above circuit is RC, 4.7kx47uf is coming to 0.22sec, i cannot reduce capacitance to an extent that time constant is close to 0.15sec after that lot of ripple. Read more

Current limiter – Inrush current – I have posted a very simple circuit to prevent inrush current. It does the job up to 27V and I don’t know why at 27V Q1 blows up. I have set the sense resistor to limit the current at 1.8A ( as it is what I would want) and it blows at 27V, and I have changed the current limit and it keeps blowing up. Read more

Help in tunable circuits – I need help in designing tunable circuits. I want to tune my circuit from 100 HZ to 500 Hz while designing filters. I have seen research articles based on electronically tunable filters but they haven’t shown the tuning circuitry. How can I tune the circuit? Can I just tune by varying the biasing voltage? Read more

SNR issue with continuous time 2nd order feedforward sigma-delta – I am designing a 2nd order continuous time feedforward sigma-delta where the input is current. the design parameters are: OSR=128, sampling frequency=1MHz, OTA gain=70dB, OTA UGBW=2.5MHz, NRZ DAC current=12uA. I have done the simulation in Simulink/MATLAB achieving 87dB SNR. But, doing the transistor level simulation in Cadence, I am showing higher noise floor than what is supposed to be. Read more

Amplifier output MOSFET protection – I designed this amplifier output protection for speakers. This circuit blocks DC output from the amplifier and is also an antibump. Originally, the circuit was using a relay, I replaced it with a MOSFET relay. There is a problem with that? In the simulation, I see no problems, but some guys say that there are additional distortion using MOSFETs at the output.

Proteus: timestep too small on a basic circuit – I would like to know what im doing wrong on this circuit cause I got an error: ([SPICE] TRAN: Timestep too small; timestep = 0.0133112: trouble with node #D1_S2#branch) and this is the most basic circuit I can make. Read more