Dear all, I have a question regarding obtaining complex outputs from the wideband spectrometer.
While going through the spectrometer design in detail, I noticed that the power block appears to compute the magnitude-squared of the complex FFT output by squaring the real and imaginary components and then summing them. [image: Screenshot from 2026-06-01 18-38-30.png] In the complex spectrometer design, the FFT output consists of: - First 24 bits: Real component (MSB first) - Next 24 bits: Imaginary component (LSB side) Since each component is multiplied by itself, the resulting products are 48 bits wide. After the summation, the output becomes approximately 49 bits (48 + 1 carry bit). My difficulty is understanding how this output relates to the subsequent *simple_bram_vacc* block, which is configured with: - BitWidth = 64 - Binary Point = 34 How are these parameters derived from the incoming data stream? A similar question arises in the real spectrometer design. There, the real and imaginary components appear to be 18 bits each, resulting in a power computation width of approximately 36 + 1 bits. However, the *simple_bram_vacc* parameters appear to remain unchanged. I am therefore trying to understand the rationale behind the BitWidth and Binary Point settings of the accumulator. [image: Screenshot from 2026-06-01 19-01-33.png] >From examining the *simple_bram_vacc (figure above the para)* and *delay_bram* *(figure above the para) *block diagrams, my current understanding is that: - A pulse is generated every *vector_length* samples (512 in this case). - During the accumulation period, the delay BRAM stores data at incrementing addresses. - The accumulation continues until the count reaches approximately *(DelayLen − bram_latency − 1)*. However, I am unsure whether this interpretation is correct. [image: Screenshot from 2026-06-01 19-11-38.png] My current goal is to modify the spectrometer to preserve and output the complex FFT values instead of computing power. If I bypass the power calculation and directly pass the complex FFT output into the accumulation stage: 1. How would *simple_bram_vacc* store the incoming complex values? 2. Would separate accumulators be required for the real and imaginary streams? 3. Is there an existing CASPER block or example design that demonstrates accumulation of complex spectra rather than power spectra? I would greatly appreciate any explanation or pointers to relevant documentation regarding this. Hoping for a response soon, Thank you, Sincerely, Nitin -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/0b14ee1f-3011-4def-a85d-8565937b855en%40lists.berkeley.edu.
