The following table shows the system requirements for the polyphase channelizer. The input sampling rate is 10.5 GSPS. The design supports M=16 channels with each one supporting 10.5G / 16 = 656.25 MHz of bandwidth. The channelizer employs a polyphase technique as outlined in [1] to achieve an oversampled output at a rate of P/Q = 8/7 times the channel bandwidth, or 656.25 * 8/7 = 750 MSPS. The prototype filter used by the channelizer uses K=8 taps per phase, leading to a total of 16 x 8 = 128 taps overall.
| Parameter | Value | Units |
|---|---|---|
| Input Sampling Rate (Fs) | 10.5 | GSPS |
| # of Channels (M) | 16 | channels |
| Interpolation Factor (P) | 8 | n/a |
| Decimation Factor (Q) | 7 | n/a |
| Channel Bandwidth | 656.25 | MHz |
| Output Sampling Rate | 750 | MSPS |
| # of taps per phase (K) | 8 | n/a |
The following figure shows a block diagram of the polyphase channelizer. The following five blocks perform the required signal processing functions:
The Circular Buffer converts the scalar input data stream into an M-vector output format for the downstream blocks, and introduces state to manage the P/Q output oversampling. Its memory depth spans the full extent of M x K samples. Conceptually, the circular buffer operates on a M x K array, employing a “serpentine shift” to introduce S = M x Q / P samples to each new output block. The remaining M - S samples come from the state history.
The Polyphase Filter implements a parallel bank of M filters across the columns of the M x K circular buffer. Each filter employs K = 8 coefficients taken from an M-phase decomposition of the channelizer prototype filter. The filter produces a single vector of M output samples.
The Cyclic Shift Buffer removes frequency-dependent phase shifts from the downstream Inverse Discrete Fourier Transform (IDFT) outputs using a memoryless and periodically time-varying circular shift of its inputs. A finite state machine (FSM) manages the sequence of input permutations across each input block. The number of states depends on the specific oversampling ratio factors P and Q and number of channels M.
The Inverse Fast Fourier Transform (IFFT) performs an IDFT operation on its input vector of M samples to produce a transformed vector of output samples. In the channelizer context, the IDFT performs a parallel bank of M frequency down-conversion operations. Each IDFT output represents a separate down-converted channel of bandwidth Fs / M sampled at a rate of Fs / M * P / Q samples per second.
The output buffer prepares the output channel samples for consumption by downstream processing. It is not included in this reference design.