A true random number generator (TRNG) which is based on interaction among frequency sources is proposed in this work. Unlike all other TRNGs which produce randomness from either harvesting physical noises or utilizing structure defect and manufacture imperfection, this TRNG generates its random number series through the interaction of multiple signal sources, each with its unique frequency. This method is enabled by the excellent frequency-generation-capability of the Time-Average-Frequency Direct Period Synthesis (TAF-DPS). This type of TRNG has the advantages of low cost, low power and the robustness against PVT and power supply variations, environmental noises and malicious attack. The all-digital nature also makes it implementation-friendly and process-portable. In this work, an implementation on FPGA is demonstrated and the resultant random data streams have passed all the NIST tests.