Integrated active integrator filter with compensated unity gain bandwidth
AssigneeNational Semiconductor Corporation
InventorLaurence Douglas Lewicki
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Abstract
An active RC integrator filter with finite operational amplifier bandwidth can be compensated by biasing the operational amplifier input stage such that its transconductance becomes a function of the resistance. Thereafter, by inserting another resistance of the same material in series with the integrating capacitor, a zero results in the overall transfer function of the filter according to the present invention. In this manner, the passband peaking of the active RC integrator filter resulting from the integrator phase shift can be avoided.
Claims20
An integrated active integrator filter circuit, said circuit comprising:
- an operational amplifier including an input node, an output node and a biasing node;
- a bias circuit including a first resistaice coupled to said operational amplifier biasing node and configured to provide a bias signal;
- and
- a feedback circuit including a second resistance and a first capacitance serially coupled between said input and output nodes;
- wherein a ratio of said first and second resistances is selected to a predetermined value for cancelling a non-dominant pole of said filter.
A method of providing an integrated active integrator filter circuit, said method comprising the steps of:
- providing an operational amplifier including an input node, an output node and a biasing node,
- providing a bias circuit including a first resistance coupled to said operational amplifier biasing node and configured to provide a bias signal;
- and
- providing a feedback circuit including a second resistance and a first capacitance serially coupled between said input and output nodes;
- wherein a ratio of said first and second resistances is selected to a predetermined value for cancelling a non-dominant pole of said filter.
A filter circuit, comprising:
- a filter input terminal;
- a filter output terminal;
- an operational amplifier having first and second input nodes, an output node and a biasing node, said operational amplifier output node coupled to said filter output terminal;
- an input capacitance coupled between said filter input terminal and said operational amplifier first input node;
- an input resistance coupled between said filter input terminal and said operational amplifier first input node;
- a feedback circuit having a feedback resistance and a first capacitance coupled between said first input node and said output node of said operational amplifier;
- and
- a bias circuit including a bias resistance coupled to said operational amplifier biasing node and configured to provide a bias signal;
- wherein a ratio of said first and second resistances is selected to a predetermined value for cancelling a non-dominant pole of said filter.
A method of providing a filter circuit, comprising the steps of:
- providing a filter input terminal;
- providing a filter output terminal;
- providing an operational amplifier having first and second input nodes, an output node and a biasing node, said step of providing said operational amplifier includes the step of coupling said operational amplifier output node to said filter output terminal;
- coupling an input capacitance between said filter input terminal and said operational amplifier first input node;
- coupling an input resistance between said filter input terminal and said operational amplifier first input node;
- coupling a feedback circuit having a feedback resistance and a first capacitance between said first input node and said output node of said operational amplifier;
- and
- coupling a bias circuit including a bias resistance to said operational amplifier biasing node and configured to provide a bias signal;
- wherein a ratio of said first and second resistances is selected to a predetermined value for cancelling a non-dominant pole of said filter.
Dependencies are inferred from the claim text.