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.
Switched capacitor equivalent of a RC low pass filter – I am trying to make the switch capacitor equivalent of an RC passive filter and compare there frequency response curves.
My 3dB frequency for the RC filter is 1KHz where C is 1pF and Req is 159 mΩ. I am using an fs of 2KHz and the C1 value comes out to be 0.5pF.
Vin value is 1.65V and clock is 3.3V when it is high. I read that for discrete time variant circuits you had to a PSS followed by PAC. This is the first time I had done both and I am attaching the forms for both analyses. I am trying to figure out why my freq response curves are different. Here I plot both the magnitude of the outputs of the RC and the switched cap circuit. The red is the former one and the blue is the latter. The switched cap (blue) rolls off faster. I was wondering if there was an issue with my design or the simulation settings. It seems the RC constant of the switch cap is larger resulting in smaller 3dB frequency. Read more
JFET buffering for oscilloscope – I want to buffer a signal from a high impedance source and shift the level of that. The frequency is about 0 to 50 MHz. The circuit I found is like this:
in software it is ok but in practice 3db point of this circuit is about 7 MHz. Since I’m new in analog design any correction for this circuit or any new circuit will be appreciated. Read more
Very simple audio activated relay (PTT) – I want to make a simple PTT driven by the sound card of the PC. I have connected a 2n7000 source to the ground and the drain to a relay coil (with internal diode) then the other contact of the relay coil to the VCC. The 2n7000 pulsates the relay on and off when I touch the gate with my finger, possibly because my hand acts as a receiver antenna for the hum in the lab. The point is, if the MOSFET is that sensitive, why can’t I make it turned on by the audio of the sound card after rectifying it with a germanium diode? Read more
Opamp gain clip the output some certain level of voltage – As a part of one of my project, am using with a differential op-amp LM741,as following circuits:
I am giving input 0 to 230-Volt ac (50Hz) directly. In this circuit .the output will be voltage clip some certain level (about 500 mV). What is the problem? Read more
Compare two voltages and select the maximum one – I need to build an analog circuit without any uP, FPGA or programmable logic device, to compare to input voltages, and provide to the output the maximum one. Can anyone tell me any recommendation to do it? Read more
Convert 0 to 10 volt into from 5 to 0 volt – I have an input volt from 0 to 10 volt and I need to change it to 0 to 5 V with reverse action.I read it as inverting amplifier specification, G = -0.5, +10V output offset. Read more
Analog optoisolator – I want a 1:1 optoisolator for the voltage ranges from 0 V to 3.3 V. Say if 1.2 V is given to the input of optoisolator. I need the same 1.2 V from the output. Is there any ready-made IC available? Read more
Ramp current generator – I have a current output chip, which can generate 1mA current. I would like to have a current with a slow ramp, for 0mA-1mA with 30s ramp time, and from 1mA-0mA with 30s ramp time as shown in the figure. How can I generate the ramp with simple other chips? Read more
MOS varactors for high frequency – I am trying to characterize MOS varactors (NMOS) to get S-parameters along with the CV-curve for this circuit. However, I am not getting a suitable result. Please have a look and point out the mistake. Read more
High voltage ignition, about 2us spark – I need High voltage ignition, not for gas or engine ignition, but for ionization of gas. I think it will require MHz switching speed.
Am I right? Read more