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Analog Switches Suitable for use in Charge Amplifiers

Question asked by Platytude on Jul 9, 2015
Latest reply on Jul 9, 2015 by Platytude

Hello,


     I'm creating a circuit to amplify charge signals given off by a piezoelectric transducer (the particular model I'm using is shown here http://www.puiaudio.com/pdf/AB2025B-LW100-R.pdf). The signal would normally be read by a charge mode amplifier (essentially a current integrator that balances the charge on the capacitance of the sensor and the feedback capacitor, Charge amplifier - Wikipedia, the free encyclopedia).

 

     My issue is that there will be a voltage pulse across the piezo sensor to excite it before the signal is read (~6V), and this voltage spike is causing problems with the op amps and their settling times, so I need a way to isolate the sensor from the amplifiers momentarily. The signals I'm trying to pick up from the sensor are small, and in the 150Khz range, so I thought an analog switch would be a good way to provide the isolation I'm looking for.

 

     My question has to do with the internal topology of the switch. A switch such as the ADG849 seems like it would be ideal, however there are a couple of things that were not present in the datasheet that I need to know. Most manufacturers seem to exclude the internal layouts of the switches, and this could potentially cause negative interactions between the switch and the charge amplifier function. For example, if the switch has internal buffering, rather than just employing the traditional MOSFET configuration, it could potentially block the feedback capacitor from seeing the sensor capacitor, and this is needed for the amplifier to work. Is there any way to obtain this information? Additionally, if anyone has experience with charge amplifiers and signal isolation in general I'd love to hear your advice.

 

Regards,

Timothy McGuire

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