Subthreshold bandgap voltage reference aiming for energy harvesting: 100na, 5 ppm/c, 40 ppm/v, psrr -88db

The proposed analog design belongs to a class of CMOS resistor free bandgap voltage (V_BG) references whose proportional to absolute temperature (PTAT) voltage (V_PTAT) is generated by summing K number of thermal voltages (V_T) via a string of K number of self-cascodes (SC). The VBG is produced by adding this V_PTAT to a complementary to absolute temperature (CTAT) voltage (V_CTAT), which is generated by base-emitter voltage (V_BE) of a parasitic vertical bipolar junction transistor (BJT) in 0.18u digital CMOS. Compared to prior art, this circuit´s contributions are: (1) The design employs similarly configured SCs in both the PTAT SC string as well as in the bandgap´s bias current (I_BIAS) circuitry, where IBIAS feeds the SCs in the PTAT string, thereby generating a stable V_PTAT over power supply and process variations; (2) AC, and transient performances are benefited because the V_PTAT and V_CTAT signal paths are made independent and in series with one another. Thus, the concurrent positive and negative V_PTAT loops inherent in conventional bandgaps, which are more prone to oscillation, are avoided; (3) Comparatively speaking, noise performance and die yield are fundamentally improved since V_PTAT is generated via summation here, instead of multiplication that is operant in conventional bandgaps. Moreover, I_DD and I_BIAS are primarily a function of MOSFET´s mobility (u) and VT, and independent of MOSFET´s threshold voltage (V_TH), which improves yield to specifications over fabrication process variations. Simulations, including monte carlo (MC) and worst-case (WC), show the following specifications are achievable: VBG ~ 1.238 V at VDD ~ 1.3 V; IDD ~ 100 nA; Voltage Coefficient (VC) ~ ±20 ppm/V; Temperature Coefficient (TC) ~ ±2.5 ppm/C with 0C <; T <; 70C; Power Supply Rejection Ratio (PSRR) ~ -88dB; Start-up time (tsu) ~ 38 millisecond; and I_DD variations ~ ±7% over process corners; die size ~ 85um/side.