This paper presents a new interpretation of the jitter-to-fast-clock-period ratio in oscillator-based true random number generators (TRNGs). This parameter, that can be employed to characterize the output random bit stream quality at the circuit level, is expressed in this paper as the product of two other parameters: phase jitter and slow-clock-period-to-fast-clock-period ratio. Based on this new expression, a strategy to increase the TRNG throughput without compromising the randomness of the output bit stream is proposed. As an example, it is presented the design of a Schmitt trigger oscillator-based TRNG in an AMS 0.35μm CMOS process, which consumes 0.6 mW, occupies 0.0396 mm2 die area and generates 400 kbps random bit streams. The obtained random sequences were tested using the National Institute of Standards and Technology (NIST) statistical test suite for random number generators validation.