METHOD AND APPARATUS FOR INTERFACING INTEGRATED CIRCUITS (ICs) THAT OPERATE AT DIFFERENT SUPPLY VOLTAGES

摘要

A Tx IC and an Rx IC that use different supply voltages are mounted on a circuit board and interfaced via traces of the board. The configuration of the Tx IC is such that DC decoupling is provided between the ICs while also preventing inadvertent turn-on of the ESD diodes of the Rx IC. These features make it possible to provide DC decoupling between high-performance Tx ICs that use relatively high supply voltages and Rx ICs that use relatively low supply voltages without the need for AC coupling capacitors and while also preventing ESD protection of the Rx IC from being degraded.

主权项

1. An integrated circuit (IC) acting as a transmitter (Tx) IC for driving at least a first pair of electrically-conductive traces of a circuit board (CB), the IC comprising:
an analog front end (AFE) portion having first and second output terminals, the AFE portion outputting a pair of output signals from the first and second output terminals; and a Tx driver circuit, the Tx driver circuit comprising a differential transistor pair, a resistive divider network, a voltage supply, a current source, and first and second output terminals, the differential transistor pair comprising first and second transistors, each transistor having at least first, second and third terminals, the first terminals of the first and second transistors being electrically coupled to the first and second output terminals, respectively, of the Tx AFE portion for receiving respective output signals of the pair of output signals outputted from the AFE portion, the second terminals of the first and second transistors being connected to one another and electrically coupled to a first terminal of the current source, the second terminal of the current source being electrically coupled to ground, the third terminals of the first and second transistors being electrically coupled to first and second input terminals, respectively, of the resistive divider network, the resistive divider network having first and second output terminals that are electrically coupled to the first and second output terminals, respectively, of the Tx driver circuit, the first and second output terminals of the Tx driver circuit being connectable to first ends of the first and second electrically-conductive traces to enable the Tx driver circuit to drive the first and second electrically-conductive traces, the resistive divider network being electrically coupled at a first node of the resistive divider network to the voltage supply and at a second node of the resistive divider network to ground, wherein the Tx driver circuit provides a Tx output common mode voltage, VTXCM, at the output terminals of the Tx driver circuit, and wherein the resistive divider network is configured to shift a level of VTXCM from a first level to a second level that is compatible with a voltage supply of an Rx IC.