Is there any problem with an inductive circuit (magnetic-field coil) on the input to the THS4524?
In the gain calculation, is the gain just Rf/Rg, where Rg is the magnitude of the impedance of the coil?
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Hello Ben,
The Inductive circuit you mentioned in the EVM are actually transformers. On the input side of EVM, these transformers are not populated even if they are shown in the schematic. On the output side, these Transformers are used to convert the differential output of THS4524 to single ended outputs.
The gain is calculated from Rf/Rg where Rf is the feedback resistor and Rg is the gain set resister. There is no Impedance of the coil coming in the gain equation since the input side of EVM is not using a transformer. Please refere to Sec 9.2.3 and 9.2.4 of THS452x Datasheet for various configurations of using THS4524.
Thanks and regards,
Eldho
Since we are operating in the kHz range, we are not using any transformers on this board.
The input signal comes from a magnetic-field sensing coil, which has a substantial inductance.
I understand that in the gain equation, Rg includes all resistance in the input circuit, including in this case, the resistance of our magnetic-field sensing coil.
Should the inductive reactance of our input coil (2*pi*f*L) be included in a vector sum with the coil R in order to calculate the Rg that is used in the gain equation?
Ben,
Yes you would just use the vector sum. You can simulate this in TINA-TI a Spice tool. Its a lot easier. The link is below. You should have some resistance on that resistor pad to isolate the PCB and trace capacitance from the input of the amplifier.