Switchable current source for digital-to-analog converter (DAC)

摘要

A switchable current source (10) for video DACs that reduces output transients. The switchable current source (10) includes a current mirror (20) connected to a cascode pair (22) for providing a reference current input and a current output. Connected to the reference current input is reference current generator (14) that includes p-channel transistor Q5 for providing a reference current according to the voltage applied at its gate by voltage source (24). A current switch (16) is connected to the current output and includes p-channel transistor Q6 for providing a path to ground and p-channel transistor Q7 for providing a path to an output node. In response to a decoder input DEC, an enable signal generator (18) outputs an enable signal EN and an inverted enable signal ENI to Q7 and Q6, respectively. The enable signal generator (18) includes a delay path (30 and 34) for both the EN and ENI signals so that during a low-to-high transition of signal DEC, EN is delayed so that ENI turns Q7 on before EN shuts off Q6. During a high-to-low transition of DEC, ENI is delayed so that Q6 is turned on before Q7 is turned off.