The U.S. dollar opened mixed on Tuesday. After hitting a one-week peak against the euro overnight, it slipped against the British pound. The single currency experienced a turbulent overnight session, falling broadly after Portugal's sovereign credit rating was slashed by a couple notches. The euro was also on the defensive after German investor sentiment declined more than expected and to its lowest since April 2009 in July.Despite those negative headlines, the single currency recovered some after a well-received Greek auction of government debt helped to allay concerns about the bloc's debt crisis. Sterling rose broadly overnight, rebounding off a July 1 low hit yesterday against the greenback, after hotter-than-expected consumer inflation in June added to the debate for higher U.K. interest rates. The higher-than-expected U.K. price pressures helped to overshadow a warning yesterday from Standard & Poor's, who said that Britain still runs the risk of a sovereign debt downgrade, despite its aggressive plan to cut its high debt burden in the years ahead. U.S. stock futures were pointing to a positive open this morning, as better-than-expected second-quarter earnings from Alcoa ( AA) yesterday buoyed investor sentiment. The Canadian dollar rose on Tuesday, as higher oil prices near $76 a barrel added to the loonie's recent upbeat tone. The U.S. and Canada this morning released trade figures for May. EUR: The euro experienced a volatile overnight session and at one point fell to its lowest in a week against the greenback. The single currency fell broadly after Moody's Investors Service cut Portugal's sovereign debt rating by two notches to A1 on concerns that is government finances will deteriorate over the near term. However, Moody's offered a stable outlook for Portugal, which many investors took as a sign of confidence in the nation's current policies to slash government debt. A poor reading on German investor sentiment had also weighed on the euro. Germany's ZEW index of analyst and investor sentiment fell more than expected to 21.2 in July, its weakest since April 2009. The forward-looking poll of economic sentiment was pressured by the impact of the eurozone's debt crisis as well as the accompanying financial market uncertainty. The data reinforced expectations that economic growth in the eurozone's biggest economy may soften after the robust activity seen during the second quarter.