Signal Processing
Stereo FM Tuner IP Core (DDC Receiver)
Direct-sampling FM receiver in RTL — DDC, CORDIC demodulation, stereo MPX decoding and multipath cancellation on one FPGA.
Overview
A complete FM receiver signal chain in RTL. The RF signal is sampled directly by a high-speed ADC — no analog IF stage — then digitally down-converted (NCO + complex mixer), decimated (CIC then FIR), and demodulated by a CORDIC phase differentiator. The 19 kHz pilot is recovered to decode the stereo multiplex, de-emphasis (75/50 us) is applied, and 24-bit audio leaves as I2S, S-PDIF or AES-EBU.
Beyond plain reception, an adaptive multipath canceller (CMA-based) continuously corrects the distortion that reflections cause — the dominant impairment in real broadcast environments. Field evaluation over 30 interleaved rounds on a live multipath channel put the fourth-generation canceller at 0.57 % median intermodulation with a 0.99 % median peak, roughly a 25-36 % improvement over the earlier generations.
The decimation ratio tracks the sample clock so that the post-CIC rate is always the same, letting one code base serve several ADC and regional configurations without touching the demodulator or audio stages. Measurement outputs — RSSI, D/U ratio, deviation, pilot level, distortion — are exposed for monitoring receivers and instrumentation.
Parametric specification
| Role | Direct-sampling stereo FM receiver / demodulator |
|---|---|
| Measured S/N | 105 dB class |
| Front end | Direct RF sampling (LVDS DDR ADC interface) — no analog IF |
| Down-conversion | 32-bit NCO tuning word + complex mixer |
| Decimation | CIC (ratio tracks sample clock) + polyphase FIR with selectable bandwidth |
| Demodulation | CORDIC phase differentiator (shared with stereo decoder) |
| Stereo decode | 19 kHz pilot detect, 38 kHz subcarrier recovery, separation trim |
| De-emphasis | 75 us / 50 us / off |
| Multipath canceller | Adaptive (CMA) with guard logic and warm re-training |
| Audio output | 24-bit — I2S (96/192 kHz), S-PDIF, AES-EBU (differential) |
| Measurement outputs | RSSI, D/U ratio, deviation, pilot level, distortion, VU |
| Control | Register/serial control (tuning, bandwidth, mute, mono, de-emphasis, RF attenuation) |
| Status | FPGA-verified on hardware, field-evaluated on live broadcast channels |
Performance
Variants
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Highest sample-clock configuration for monitoring and measurement receivers.
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Alternate sample clocks for regional band plans — the decimation set is swapped, the rest of the chain is unchanged.
Deliverables
- Synthesizable VHDL RTL — DDC, decimation, CORDIC demodulator, stereo decoder, audio output stages
- Adaptive multipath canceller with control FSM
- Integration guide, register map and timing constraints (on request)
- FPGA reference build and measurement procedure
Supported Devices
Targets / verified platforms. ASIC process numbers are characterized at integration.
The same direct-sampling DDC chain — NCO tuning, decimation, CORDIC phase extraction — is the core of NMR and MRI receive paths, where narrow-band signals must be recovered from a high-rate digitized RF stream. The FM configuration is the broadcast instance of that architecture.
Measured figures are from the reference FPGA build and live-channel field evaluation; final performance depends on the ADC, RF front end and board design of the target system. Detailed specifications and evaluation data are available on request.
Documents
Full datasheet, integration guide and evaluation files are available on request. Request access below — we reply within one business day.
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