A Class-G Headphone Amplifier in 65 nm CMOS Technology

This paper presents a class G amplifier based on a low distortion switching principle technique called switching currents injection. The switching circuit enables a very smooth handover between the voltage supply rails obtaining both high efficiency and low distortion. An approach for the evaluation of the switching distortion in a class G amplifier (and the ability of the loop to reject it) is proposed and the results obtained are used to optimize the overall distortion after compression by the feedback loop. The integrated 65 nm CMOS class G headphone driver based on the above concept operates from $pm $1.4 V and $pm $0.35 V supplies. At low power level it uses almost exclusively the low voltage supply reducing the dissipation to 1.63 mW @ ${rm P_{rm out}}= $0.5 mW into 32 $Omega$. At higher power level, where both supplies are used, the smooth transition between the rails allows a ${rm THD}+{rm N}$ better than ${-}$80 dB for ${rm P_{rm out}}leq $16$~$ mW into 32 $Omega$ . The SNR is 101 dB, quiescent power is 0.41 mW and active die area is 0.14 mm$^{2}$.