Randy Jackson's Wife -- I Want A Divorce, Dawg!

Ex-"American Idol" judge Randy Jackson just got voted out ... of his marriage. His wife filed for divorce ... TMZ has learned.

Erika Jackson filed docs to end their 18-year marriage ... citing irreconcilable differences.

She wants full physical custody and joint legal custody of the 1 minor son, 17-year-old Jordan. They have a daughter who is an adult.

Erika also wants spousal support and she wants him to foot her attorney's fees.

This is Jackson's 2nd marriage. He has 1 other daughter from his prior marriage.

Jackson spent 12 seasons judging "American Idol" ... but announced he was leaving in 2013. He later returned as a musical mentor for the contestants.