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Closed Loop Continuous Source Follower For Level Shifter Between Two Supply Voltages

IP.com Disclosure Number: IPCOM000013144D
Publication Date: 2003-Jun-16
Document File: 3 page(s) / 121K

Publishing Venue

The IP.com Prior Art Database

Abstract

Methods and apparatus for level shifting an input signal received by an input receiver stage where two supply voltages are being used. Closed loop feedback may be used to track out variations between the two supply voltages of input devices by varying a biasing current source in a source follower circuit being used as the input stage of the input receiver transistor. A duplicate of the receiver is coupled to a comparison circuit in a closed loop system including an operational amplifier, current mirror and dominant pole capacitor to provide an accurate biasing voltage for other input receivers. A first transistor, whose gate is tied to the I/O power supply, is configured in a source follower configuration, with a second transistor acting as a current source. An Operational amplifier compares the second power supply (e.g., the internal power supply) and the voltage level produced from the source follower circuit. The output is integrated using a dominant pole capacitor which will dictate the loop frequency level to produce a compensated bias voltage for all input receivers used on an integrated circuit device.

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Closed Loop Continuous Source Follower for Level Shifter Between two Supply Voltages

                           Methods and apparatus for level shifting an input signal received by an input receiver stage (e.g., where two supply voltages are being used). In an embodiment, closed loop feedback is used to track out variations between the two supply voltages of input devices by varying a biasing current source in a source follower circuit being used as the input stage of the input receiver transistor. The level shifting circuit of a specific embodiment is shown in figure 1 below. With reference to figure 1, a duplicate of the receiver (N1) is coupled to a comparison circuit in a closed loop system including an operational amplifier, current mirror and dominant pole capacitor to provide an accurate biasing voltage for other input receivers. The transistor N1, whose gate is tied to the I/O power supply, is configured in a source follower configuration, with transistor (N2) acting as a current source. Operational amplifier (OA1) compares the second power supply (e.g., the internal power supply) and the voltage level produced from the source follower circuit. The output is integrated using the dominant pole capacitor which will dictate the loop frequency level to produce a compensated bias voltage for all input receivers used on an integrated circuit device. In more detail, when the source node voltage of N1 is higher than the supply voltage applied to the other input of OA1, the output of OA1 wi...