Circuitry generates base-to-emitter voltages (Vbe1, Vbe2) of two BJTs biased at different current densities, a base-to-emitter voltage (Vbe) of a BJT biased so Vbe is complementary to absolute temperature and has a curved non-linearity across temperature, and base-to-emitter voltages (Vbe1_c, Vbe2_c) of two BJTs biased by a temperature independent constant current and a current proportional to absolute temperature so Vbe2_c−Vbe1_c has the same but opposite curved non-linearity across temperature as Vbe. A sampling circuit samples these voltages and provides them to inputs of a loop filter. Filter outputs are quantized to produce a bitstream. The sampling circuit: when the received bit of the bitstream is zero, causes integration of Vbe1−Vbe2 to produce a voltage proportional to absolute temperature (αΔVbe); and when the received bit of the bitstream is one, causes integration of Vbe2_c−Vbe_Vbe1_c to produce a negative voltage complementary to absolute temperature −Vbe_c without non-linearity across temperature.