Cypress Semiconductor Corporation

Mohandas Palathol Mana Sivadasan

Gajender Rohilla

Anil Agarwal

A method and test circuits for measuring skew between two circuit blocks of an integrated circuit. A first data signal is propagated through a first circuit block and a first clock signal is propagated through a second circuit block. The first data signal is latched synchronized to the first clock signal after propagating the first data and clock signals. The first data signal is time shifted relative to the first clock signal until the first data signal is no longer validly latching. A second data signal is propagated through the second circuit block and a second clock signal is propagated through the first circuit block. An inversion of the second data signal synchronized to an inversion of the second clock signal is latched. Then, the second data signal is time shifted relative to the second clock signal until the inversion of the second data signal is no longer validly latching.

Circuit to measure skew

One embodiment of the present invention is an improved feedback amplifier circuit having a variable closed loop gain which avoids including switching elements in its feedback network and maintains a constant output voltage window for an input signal having a wide dynamic range. That is, the switching elements are not on the active feedback path (e.g., they are isolated from the active feedback path). In this manner, the gain of the amplifier circuit may be determined only by the feedback resistance which can be more easily controlled through the use of precision resistors. Additionally, by removing the switches from the feedback network, the parasitics associated with each switch may also be removed from the feedback path of the amplifier circuit. Accordingly, the bandwidth of the feedback amplifier circuit can be controlled more effectively. Specifically, the present embodiment avoids locating the switching functionality in the feedback network by changing the output stage of the feedback amplifier circuit. In other words, the switching functionality of the present embodiment is located within the output stage of the feedback amplifier circuit. Furthermore, it is appreciated that the present embodiment provides a way to isolate the unused feedback path of the feedback amplifier circuit which has a variable closed loop gain.

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Bengaluru, India

Mohandas Palathol Mana Sivadasan