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Comedian Bill Cosby, who is serving a three and a half year jail sentence, on Tuesday appealed a Pennsylvania court's verdict that found him guilty of drugging and sexually assaulting a woman 15 years ago.

"This filing is an important step in ensuring that Mr Cosby receives a hearing from a fair and impartial court," the actor's spokesman, Andrew Wyatt, said.

"The Constitution guarantees that right to Mr Cosby -- and to all Americans -- and he looks forward to securing justice in the court of appeal," he said in a statement.

The 81-year-old, who shattered racial barriers with his pioneering role as a dad and doctor on the hit television series The Cosby Show, (1984-1992), was found guilty in April 2018 of drugging and sexually assaulting Andrea Constand, now 46, at his Philadelphia mansion.

It was the first trial and first guilty verdict for sexual assault since the advent of the #MeToo movement.

An earlier trial in June 2017 ended in a mistrial after the jury was unable to reach a unanimous verdict.

In September 2018, a Pennsylvania judge sentenced the actor to three and a half years in prison on three counts of aggravated indecent assault: penetration without Constand's consent; penetration when she was unconscious and penetration after having been drugged. He was immediately incarcerated.

Although more than 60 women charged that they had been victims of sexual assault by Cosby, the famous comedian was tried criminally only for Constand's assault, since the statute of limitations had expired in the other cases.

Cosby insists he was unjustly convicted.

"America will be great when it fulfills the last four words of the revered Pledge of Allegiance .... 'and justice for all,'" Cosby's wife Camille said in the statement.

A dozen women who say they were victims of Cosby have filed civil suits against the actor seeking compensation for damages.