Practical Optimization of EMI Reduction in Spread Spectrum Clock Generators With Application to Switching DC/DC Converters

Abstract

We here consider the most common technique used in spread spectrum clock generators, that is the frequency modulation of a timing signal by means of a triangularly shaped waveform. As a first step, we develop a reliable mathematical model of a spectrum analyzer, which allows us to compute the power spectrum as measured by this instrument for any signal put at its input. This is particularly important when considering spread spectrum clocking methods for electromagnetic interference reduction, since international regulations impose constraints on the peak of the spectrum of interfering signals as measured by this instrument. Thanks to the developed mathematical tool, we are able to theoretically prove that the maximum peak reduction of the measured spectrum is achieved for a well defined frequency of the triangular driving signal. This is in contrast with what one can obtain by optimizing the theoretical power density spectrum, where the minimum interference is ideally obtained when the triangular signal has a vanishing frequency. Results are confirmed by measurements on two commercial DC/DC switching converters.

Spread spectrum modulation investigation using MATLAB developed tool on automotive DC-DC converter

“…A similar concept was tried on switching DC-DC converters by F. Lin and D.Y. Chen, from Virginia Power Electronics Center (VPEC) [23][24][25][26][27][28]. Nevertheless, many research works applying SSFM to DC-DC converters, used various modulation profiles such as sinusoidal and random, but authors did not extend in-depth the effects of possible modulation with other periodic profiles.…”

“…In such publications, the theoretical basis of SSFM using periodic profiles was established and the method was applied on the PWM control signal. The triangular profile showing that maximal flat spectrum can be obtained and that selective cancellation of harmonics is possible with certain exponential profiles [28]. In this research work, comparison between the theoretical and experimental results of [29] to [30] with experimental results measured at the supply of a low power (2,5W) buck converter switching at =1MHz [35].…”

Reconfigurable bi-frequency DPWM with custom spectral shaping in a synchronous buck converter

“…Variable switching frequency operation was proposed in [11]. Periodic switching frequency modulation schemes were investigated in [12]- [14]. A bi-frequency scheme was introduced in [15], in which time periods are generated using variable frequency approaches, such constant on-time and constantoff time control, which require separate hardware resources in digital implementation.…”

Direct Sequence Spread Spectrum-Based PWM Strategy for Harmonic Reduction and Communication

“…In [15], a pseudorandom sequence is employed in frequency hopping spread spectrum modulation to reduce the spectral power density at the harmonic frequencies. In [24][25][26], triangular and bi-frequency periodic modulation techniques are adopted for custom spectral spreading with predictable parameters. In the above cited papers, spread spectrum techniques are only used for mitigating EMI issues, but not for communications.…”