Method and apparatus for a direct current (DC) coupled input buffer
AssigneeXilinx, Inc.
InventorsBrian T. Brunn, Michael A. Nix, Ahmed Younis
Life of this patent
Estimating the term…
Abstract
A method and apparatus for combining an alternating current (AC) coupling technique with a low frequency restoration technique to provide AC coupling with low frequency restoration of the attenuated low frequency content. The low frequency restoration circuit operates to extract low frequency information prior to being high-pass filtered by the AC coupling circuit. The low frequency restoration circuit then buffers the low frequency information through a low frequency restoration amplifier, applies a programmable common mode voltage to the buffered, low frequency information, and then restores the buffered, common mode adjusted, low frequency information to the output of the AC coupling circuit.
Claims17
An input buffer, comprising:
- an alternating current (AC) coupling circuit coupled to receive a first signal at a first node and adapted to provide a second signal to a second node in response to the first signal, the second signal exhibiting attenuated frequency content below a first frequency, the alternating current coupling unit comprising:
- a first capacitor having a first conductor coupled to the first node and a second conductor coupled to the second node;
- and a first resistor having a first conductor coupled to the first node;
- and
- a frequency restoration circuit coupled to receive the first signal at the first node and adapted to provide a third signal to the second node in response to the first signal, the third signal exhibiting frequency content above the first frequency, wherein the third signal is summed with the second signal at the second node to restore the attenuated content of the second signal, the frequency restoration circuit comprising:
- a buffer having a first input coupled to receive the first signal and a first output coupled to provide the third signal;
- a second resistor having a first conductor coupled to the first node and a second conductor coupled to the first input of the buffer;
- a third resistor having a first conductor coupled to the first input of the buffer and a second conductor coupled to the first output of the buffer;
- and
- a fourth resistor having a first conductor coupled to the first output of the buffer and a second conductor coupled to the second node.
A differential input buffer, comprising:
- an alternating current (AC) coupling circuit coupled to receive a differential signal at first and second input nodes and adapted to attenuate the differential signal below a corner frequency to form a high-pass filtered signal, the high-pass filtered signal being applied to first and second intermediate nodes;
- and
- a low frequency restoration circuit coupled to receive the differential signal at the first and second input nodes and adapted to attenuate the differential signal above the corner frequency to form a low-pass filtered signal, the low-pass filtered signal being applied to the first and second intermediate nodes, wherein the AC coupling circuit sets the corner frequency for both the AC coupling circuit and the low frequency restoration circuit.
A method of providing direct current (DC) coupling of an input buffer, comprising:
- receiving an input signal;
- attenuating frequency content of the input signal below a corner frequency to provide an alternating current (AC) coupled signal to an intermediate node;
- attenuating frequency content of the input signal above the corner frequency to provide a DC coupled signal to the intermediate node;
- summing the AC and DC coupled signals together at the intermediate node;
- and
- driving a differential amplifier with the summed signal to provide an output from the input buffer;
- and
- applying a programmable common mode voltage to the summed signal at the intermediate node to properly bias the differential amplifier.
Dependencies are inferred from the claim text.