Does a convicted defendant have a right of appeal against his sentence?

Convicted defendants generally enjoy a right of appeal under state law. (Pen.Code, 1237.) If they can waive this right at all, they must do so "knowing[ly], intelligent[ly] and voluntar[il]y." (People v. Vargas (1993) 13 Cal.App.4th 1653, 1657, 1659, 17 Cal.Rptr.2d 445.) Defendant seems not to have made his purported waiver knowingly. His claim of disproportionality depends in part on the sentences meted out to his codefendants. It appears that he was not aware of such sentences at the time of his purported waiver. (See People v. Vargas, supra, 13 Cal.App.4th at pp. 1662-1663, 17 Cal.Rptr.2d 445.)