Hi guys
I have designed a small pcb for a data acquisition system involving NI-DAQ. This board is primarily housing a low noise pre-amplifier(Opamp AD8613 from Analog Devices) for the DAQ and its related power circuitry. I have used a dual-supply configuration for the opamp supplying +/-1.8V. The +1.8V comes from an LDO and the -1.8V comes from a Positive-to-negative converter(ICTL7660,TI-Switched Capacitor voltage converter). I have also added first order-RC filters to limit the response in the range of 100Hz to 10Khz.
The main application of this board is to reduce the noise being coupled into the data-acquisition system. On analysis the frequency response at the output of the opamp, there are certain harmonics starting from f=3.3Khz. Subsequently, i can find them @ 2f, 3f, 4f etc. I am not sure about the source of these harmonics but they are definitely not desired.
How to go about identifying the source of these harmonics and how to eliminate them? Currently i am looking at eliminating the switch-cap converter and instead directly feed from the battery. Any other suggestion? Please help me out.
I have tried to squeeze in as much info as possible. Please let me know if any further details regarding the board is required
I have designed a small pcb for a data acquisition system involving NI-DAQ. This board is primarily housing a low noise pre-amplifier(Opamp AD8613 from Analog Devices) for the DAQ and its related power circuitry. I have used a dual-supply configuration for the opamp supplying +/-1.8V. The +1.8V comes from an LDO and the -1.8V comes from a Positive-to-negative converter(ICTL7660,TI-Switched Capacitor voltage converter). I have also added first order-RC filters to limit the response in the range of 100Hz to 10Khz.
The main application of this board is to reduce the noise being coupled into the data-acquisition system. On analysis the frequency response at the output of the opamp, there are certain harmonics starting from f=3.3Khz. Subsequently, i can find them @ 2f, 3f, 4f etc. I am not sure about the source of these harmonics but they are definitely not desired.
How to go about identifying the source of these harmonics and how to eliminate them? Currently i am looking at eliminating the switch-cap converter and instead directly feed from the battery. Any other suggestion? Please help me out.
I have tried to squeeze in as much info as possible. Please let me know if any further details regarding the board is required