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AD9954: Need to generate a quadrature signal synchronized to the output of the AD9954

Question asked by David@ on Jul 28, 2016
Latest reply on Aug 10, 2016 by JLKeip



I have put/found my self in a bad situation, while designing a LCRZ-meter I researched several techniques and originally I was going to use 2 ADCs precisely timed to the DDS output of the AD9954. But since the design calls for a excitation signal with a frequency up to 1MHz I tried to avoid having to deal with a 10MSPS speed system by using a Lock-In Amplifier(LIA), I only learned about LIAs when I where confronted by the possibility to use them to solve the complex impedance measurement and I'm sure you could do it in other way's but to the best of my knowledge I will have to use a Dual PSD(Phase Sensitive Detector) LIA where the 2 PSD's is driven by a square-wave reference signal separated by a 90deg phase difference.


I explored generating the reference signals using the AD9954 sine-wave as a starting point and then by using comparators/XOR-gates/D-type Flip-Flops I generated two square-waves one of which had a phase difference of 90deg referenced from the first square-wave. But a LIA will not tolerate such a circuit due to it adding delays and such to the reference signal's so it is no longer synchronized to the sine-wave excitation signal...


I've talked to people whom have done this sort of design but they where using FPGA's and as such could generate all the required signals from the same source at the same time, I am restricted to microcontrollers and I need 12-bit output DAC in the AD9954 DDS.


I have tried to find another AD DDS IC to be synchronized to the AD9954 to be used to output a reference signal with a 90deg phase shift but I haven't found a suitable one, it would feel weird to be forced to use a second AD9954 to generate the phase-shifted reference signal, they aren't cheap.


Do anyone know of a solution for this situation?

Or have I run into a brick wall and need to turn around and go back to the high-speed synchronized ADC sampling solution?


I would really appreciate any input on this what so ever.