| 摘要 |
In accordance with the present invention, an auto-biased cascode current circuit capable of improved range in headroom is disclosed. In one embodiment, the current circuit includes a current mirror and a bias circuit, where the current mirror contains a reference leg and an output leg. A reference current flows within the reference leg. Included in the output leg is an output terminal, a first output transistor and a second output transistor. The output terminal operates at an output potential. The bias circuit regulates the reference leg of the current mirror such that the output potential is substantially equal to a drain-to-source saturation voltage of the first output transistor plus a drain-to-source saturation voltage of the second output transistor plus a predetermined overdrive voltage. The predetermined overdrive voltage is a design parameter which is less than a threshold voltage. Even as the reference current changes, the bias circuit regulates the reference leg so that the reference current may change significantly while the bias circuit still maintains a proper output potential. In another embodiment, a method for auto-biasing a cascode current circuit is disclosed. The method detects at least one voltage potential from the reference leg and uses this information generate a cascode potential to bias the reference leg.
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