Switchable DAC with current surge protection

In a digital-to-analog converter (DAC) having a plurality of stages, each of said stages having a current source coupled to a first and a second transistor which are operable as a differential pair, a method of operating said DAC in a normal operating mode and in a sleep mode comprising the steps of:

• applying a potential to said first and said second transistors so as to render both of said first and said second transistors nonconductive when said DAC is operated in the sleep mode;
• and
• allowing current to flow from said current source through at least one of said first and second transistors when said DAC is operated in the DAC's normal operating mode.

In a digital-to-analog converter (DAC) having a plurality of stages, each of said stages having a current source coupled to a reference voltage transistor and a data input transistor which are operable as a differential pair, an apparatus for selectively switching said DAC between a normal operating mode and a sleep mode comprising:

• means for coupling the data input transistor to a source of data;
• and
• means coupled to said current source and said reference voltage transistor which is responsive to a control signal for switching said DAC to its normal operating mode when said control signal is at a first logical level and for switching said DAC to the DAC's sleep mode when said control signal is at a second logical level.

In a digital-to-analog converter (DAC) having a plurality of stages, each of said stages having a current source coupled to a reference voltage transistor and a data input transistor which are operable as a differential pair, an apparatus for selectively switching said DAC between a normal operating mode and a sleep mode comprising:

• means for providing a bias voltage to the gate of said current source transistor and a reference voltage to the gate of said reference voltage transistor when said DAC is switched to the DAC's normal operating mode;
• and
• means for removing said bias voltage from the gate of said current source transistor and said reference voltage from the gate of said reference voltage transistor when said DAC is switched to the DAC's sleep mode.