A 460MHz at 397mV, 2.6GHz at 1.3V, 32b VLIW DSP, embedding FMAX tracking

Wide-voltage-range-operation DSPs bring more versatility to achieve high energy efficiency in mobile applications to increase signal processing complexity and handle a large range of performance specifications. This paper describes a 32b DSP fabricated in 28nm UTBB FDSOI technology [1]. Body-bias-voltage (V
_BB
) scaling from 0V up to ±2V (Pwell/Nwell) decreases the DSP core V
_DDMIN
to 397mV and increases clock frequency by +400% at 500mV and +114% at 1.3V. In addition to technology gains, dedicated design features are included to increase frequency over the full V
_DD
range, considering parameter variations. As depicted in Fig. 27.1.1, the 32b datapath VLIW DSP is organized around a MAC dedicated to complex arithmetic and two dedicated operators: a cordic/divider and a compare/select. Data enters the circuit through a serial interface and code is run from a 64×32b register file. It has been shown in [1] that a given operating frequency can be achieved at a lower V
_DD
in UTBB FDSOI compared to bulk by applying a forward-body bias. An additional design step is achieved in this work by (1) increasing the frequency at low V
_DD
thanks to a specific selection and design of standard cells with respect to power vs. performance and (2) dynamically tracking the maximum frequency to cope with variations.