Fig. 1

(a) 13 level output is proposed in ref¹⁷, (b) presented in¹⁸ and generated 13 level output, (c) four sources with nine level output presented in¹⁹, (d) Asymmetrical-based nineteen-level voltage generated with three sources referred in²⁰, (e) Asymmetrical-based thirty-one-level voltage generated with four sources referred in²¹.