Bias circuit having second order process variation compensation in a current source topology

摘要

A bias circuit includes second order process variation compensation in a current source topology having a compensation transistor operating in saturation mode as a current source. An additional compensation transistor is biased to operate in a linear mode to provide an active resistor to vary a control voltage applied to the saturation mode compensation transistor and widen the range of sourced control current, thus widening the achievable range of the control voltage applied to the biasing transistor to produce a predetermined level of bias current despite process variations. The additional compensation transistor has been shown to be able to compensate for another approximately 20-25% of the induced variations leaving less than approximately 10% and preferably less than 5% variation in the bias current from the predetermined level at certain bias conditions and over typical fabrication process variations.

主权项

1. A bias circuit for producing a predetermined level of bias current, said bias circuit comprising:
a biasing transistor having a first control electrode and first and second channel electrodes, said biasing transistor operating in saturation mode to produce a predetermined level of bias current corresponding to a first control voltage applied between the first control electrode and one of said first and second channel electrodes; and a control circuit comprising,
a resistive control path;a first compensation transistor of the same type as the biasing transistor, said first compensation transistor biased to operate in saturation mode as a current source to produce a control current that flows through the resistive control path to apply the first control voltage to the biasing transistor; anda second compensation transistor of the same type as the biasing transistor, said second compensation transistor biased to operate in a linear mode as an active resistor to vary a second control voltage applied to the first compensation transistor to alter the control current and vary the first control voltage applied to the biasing transistor to produce the predetermined level of bias current.