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- 15.3.12. Fully-Parallel FFTs with Flexible Ordering (FFT2X, FFT4X, FFT8X, FFT16X, FFT32X, and FFT64X)
- 15.3.13. General Multitwiddle and General Twiddle (GeneralMultiTwiddle, GeneralMultVTwiddle, GeneralTwiddle, GeneralVTwiddle)
18.104.22.168. NCO Block Phase Increment and Inversion
To achieve a desired frequency (in MHz) from the NCO block, you must specify a phase increment value defined by:
Phase Increment Value = Frequency * 2Accumulator Bit Width / Output Data Rate
This value must fall within the range specified by the Accumulator Bit Width parameter. For example, for an accumulator bit width of 24 bits, you can specify a phase increment value less than 224.
You can specify the phase increment values in a vector format that generates multichannel sinusoidal signals. The length of the vector determines how many channels (frequencies) of data are generated from the NCO block. For example, a length of 4 implies that four channels of data are generated.
When the design uses the NCO for super-rate applications (NCO frequency is higher than output data rate), for example direct RF DUC, use multiple channels (in evenly distributed phases). The phase increment value is:
Phase increment value = mod((frequency)/(output data rate), 1)×2accumulator bit width
The modulus function limits the phase value to less than 1 and prevents interfering with the inversion bits.
When the input is in matrix format (with multiple rows of vectors), the design configures the NCO block as a multi-bank NCO for frequency hopping for multicarrier designs. The number of rows in the matrix represents the number of banks of frequencies (of sine and cosine waves) that generate for a given channel. An additional bank input and b output port automatically add to the NCO block.
You can also use the Phase Increment and Inversion parameter to indicate whether the generated sinusoidal signals are inverted. For an accumulator width in bits of 24 bits, you can add two bits (the 25th and 26th bits) to the phase increment value for a given frequency. These bits indicate if the sine (26th bit) and cosine (25th bit) are inverted.
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