A Fully Synthesizable Ultra- ${N}$ Audio Frequency Multiplier for HDMI Applications

This brief develops a highly programmable and fully synthesizable large-N frequency multiplier. It is based on Time-Average-Frequency Direct Period Synthesis (TAF-DPS) and its purpose is to generate audio frequencies in HDMI (high definition multimedia interface) applications in which frequency multiplication ratio is extremely large. The proposed multiplier is a full digital feed-forward frequency control loop. The output frequency is produced by performing a fractional frequency division of the oscillator clock with TAF-DPS. The source of electrical oscillation in the TAF-DPS is a free-running inverter ring that consists of inverters. The novel structure is implemented in a TSMC 0.18 μm 1P6M CMOS process. The implementation is fully digital HDL coding → simulation → synthesis → place & route without any need for analog simulation. The hardware cost is equivalent to 3150 two-input NAND gates. The proposed structure can achieve fast frequency switching within two input reference clock cycles. The multiplication ratio is evaluated experimentally to be as high as 106 with an input signal of 50 Hz; this is the largest ratio and lowest input frequency to be reported to the best of our knowledge. Besides generating an audio clock for HDMI applications, this frequency multiplier is very suitable for frequency measurements and system-on-a-chip applications.