The Santiago Times has a well-researched feature story on Chile’s Constitution, a holdover from the Pinochet regime (http://www.santiagotimes.cl/chile/politics/23577-ecuadors-example-sparks-debate-on-chiles-constitutional-reform).
The charter was ratified in a controversial plebiscite in 1980, which also extended Pinochet’s rule for another eight years. Subsequent governments have managed to amend some of the antidemocratic provisions, such as the appointment of non-elected members of the Senate. Other authoritarian features, such as the state security law and a binominal electoral system, remain in place.
The binominal electoral system operates in the following way: in congressional elections each district votes for two candidates, and in order to get both seats a political party or coalition must get at least two-thirds of the ballots cast—otherwise the second congressional seat goes to the candidate from a rival political party who won the most votes. Which means that quite a few members of the Chamber of Deputies and the Senate were backed by a minority of voters while more popular candidates were pushed aside.
Polls suggest that a majority of Chileans have a rather jaundiced view of their legislative branch. A poll by Adimark http://www.adimark.cl/es/estudios/documentos/002ev_gob_feb012_.pdf released last month showed that the Chamber of Deputies had a 67 percent disapproval rating, with a 63 percent disapproval rating for the Senate.