The Swiss National Bank chairman has resigned abruptly, bowing to a public uproar over his private currency deals.

Philipp Hildebrand's decision comes just as a Swiss parliamentary committee is preparing to grill him behind closed doors.

His resignation took effect immediately on Monday, Switzerland's central bank said in a brief statement.

A short time later, Hildebrand called an impromputu press conference in the Swiss capital of Bern, where he emphasised that he was proud of his achievements at financial institutions in Switzerland and international organisations such as the World Bank.

"I would like to think I have been a damn good central banker," Hildebrand said.

"I personally advocated strongly and early for stricter capital requirements for the big banks. The policy of the central bank was a success in recent years."

For the past week, Switzerland has been awash with reports about public unease over the dollar swaps last year that earned Hildebrand and his wife, a former currency trader, tens of thousands of dollars in profits at the same time Hildebrand was working to lower the value of the soaring Swiss franc.

It was his second news conference in less than a week.

Breach of rules denied

Hildebrand first broke weeks of silence Thursday to deny any breach of central bank rules and announce he was donating the trades' profits to charity.

But questions remain about the propriety of the trading, and his departure came just before he was to face a Swiss parliamentary committee on Monday seeking answers about the deals he engaged in while leading efforts to soften the Swiss franc.

Hildebrand acknowledged the past few weeks have been "a difficult time".

Legislators on the Committees for Economic Affairs and Taxation were holding the confidential session to examine questions such as whether Hildebrand and his wife traded currency from accounts other than the one at Basel-based Bank Sarasin.

But Hildebrand said he was still appearing before the legislators.

Details of the Hildebrands' trading were leaked by an IT support employee at the bank, who was apparently concerned about the possibility of insider trading.

The Swiss National Bank had cleared Hildebrand of any wrongdoing in a report in late December.