Electromagnetic field sensing – I am trying to sense an electromagnetic filed created by an iron-core coil from a distance of 12 feet. For testing, I just connect both ends of Rx coil to the scope. I get very strong signals when the Rx coil is line with either end of the Tx coil because iron core amplifies the magnetic field on both ends of Tx coil . I did some FEMM simulation and it shows that the magnetic field should extend outwards beyond 14 feet. But I don’t see any signal or the FFT function of the scope doesn’t show any spike at 25 Hz beyond 1 foot , although when Rx coil is inline with the end of TX coil I do see signal embedded in the noise. But my requirement is that Rx coil should detect 25 Hz when place 12 feet away in length-wise parallel to the Tx coil. Read more
What is the value of R1 in this op-amp circuit? – What is the value of R1 in this formula for Vout calculation for this circuit?
Vout = Rf/R1
The input is 110 V DC where Gnd of 110 V to SGNL_N is given to SGNL_P. Read more
How do you set a node to a particularly voltage? – I am designing a circuit where the requirement is that if the signal crosses a particular threshold (i.e. Vref) then the signal should settle to -Vsat. I am trying the topology below but it is not working. Any comments? Read more
SAR ADC unit cap selection – I have seen in some papers that for SAR ADCs with 10- to 12-bit resolution, the unit cap chosen was pretty small (ranging from 4 fF to 40 fF). Though this value satisfies the thermal noise or matching requirement, I think there should be a problem with input capacitance of the comparator.
For such resolutions, the input pair of the comparator can’t be small (due to thermal, flicker, and mismatch requirements), so the input cap would be large. Part of this input cap would be input dependent and will cause non-linearity effects, so the INL or DNL would be large. However, I have seen some works with a small unit cap with acceptable DNL. I’m confused. Is there something I’m missing? Read more
Op amp malfunction in SallenKey filter configuration with gain – I am designing a data acquisition system for RTDs, for which I used this application note for the analog portion. I used the ADA4004-2 op amps instead of MCP609. The application note used 7.47 gain V/V while Ii used 8 V/V. Moreover, I added another gain stage (just a simple non-inverting gain) after the filter+gain stage. The gain value for next stage is 2.5-5 V/V. The issue is that the op-amp used in SallenKey+gain configuration keeps on malfunctioning after some time or is permanently damaged giving a saturated value of +15 V or -15 V. When I replace this op amp, the new one starts working fine until it faces the fate of the old one. I am also multiplexing the RTDs and the unconnected ones produce a saturated value at the output. Can this be the reason of short life of my op amps? Read more
Leave a Reply
You must be logged in to post a comment.