Precision Tone Decoder

The TONE_DEC IP Core is a precision tone decoder with the ability to support either real or complex data samples. Samples are first mixed down to baseband before subsequent filtering and tone detection.

The centre frequency of the tone is fully programmable and is generated by a local oscillator (DDS). The DDS has an SFDR of better than 80 dBs (with phase dithering) and a theoretical SNR of approximately 100 dBs.

After down-conversion, the I and Q signal paths are filtered to remove components above the tone of interest. The characteristics of these filters may be changed depending on the desired detection bandwidth and response time.

Finally, a power function is used to compute the relative magnitude of the signal after filtering. If the complex input signal contains the tone of interest, then the relative output magnitude, mag_out, will be greater. The input threshold signal is a 32-bit unsigned integer that generates the tone_present flag when the magnitude is greater than this value. The threshold signal may be programmed in real time.

• Synthesizable, technology independent soft IP Core for FPGA, SoC and ASIC
• Supplied as human readable VHDL (or Verilog) RTL source code
• 16-bit signed input and output data samples
• Accepts either complex or real inputs
• Precision Digital Down Converter with 80 dB SFDR
• DDS Frequency resolution of FS / 232
• DDS Phase resolution of 2π / 212
• Programmable tone centre frequency and detection bandwidth
• Choice of different low pass filter responses

• Touch tone decoding (e.g. DTMF tones)
• Precision frequency monitoring and control
• Security systems and remote control units
• Complex digital down conversion
• Basic building block in FSK / OOK / ASK demodulation