Capacitor for audio high-pass filter – I’m working on an audio circuit that will run from a 9V battery and requires a high pass filter, to reduce 50-60Hz noise/hum. The pass band is specified as 180Hz to 2400Hz. The present design has a 2nd order filter and the hum is unacceptably high. What kind of capacitor is reasonable for this application? Read more.

Suppressing sudden spikes in a circuit –   I have sensor which gives me the voltage range of 0 to 10V by converting it into 0 to 5V and providing it to ADC and from ADC I’m reading it using 8051. My problem is the sensor which I’m using tends to give me some sudden spikes intermittently. I need a suggestion to suppress the spikes from the sensor and get the true sensor reading. Read more.

Measurement of phase difference – I am trying to calculate the phase difference in a sine wave with a frequency of 10KHz and amplitude of 100mV. The resistor and capacitor are in a series. The capacitor is creating a phase difference that I can see in the in the simulation I uploaded. What can I use to calculate the phase difference in terms of voltages that can read by the ADC of a microcontroller? Read more.

What is the role of the interpolation filter in a digital audio amplifier? – I wonder why we need an interpolation filter in a digital audio amplifier. Oversampling can be performed through a digital delta-sigma modulator, so PCM signals from a DSP can be oversampled after the modulator. Why do we need the interpolation filter in front of the delta-sigma modulator? Read more. 

Low pass filter design with fast attenuation rate – I’m looking at doing a design that will have a cut off frequency of around 2-3Khz with a fast attenuation rate. The components need to be passive and it also needs to block DC. I’ve tried an LC filter (4mH with 3.5uF) with a DC blocking cap in series but the attenuation rate it quite slow. Any ideas? Read more.