ON-CHIP TEST FOR INTEGRATED AC COUPLING CAPACITORS

摘要

Apparatus, method and computer program product for determining presence and relative magnitudes of on-chip AC coupling capacitors in a high-speed differential receiver device. A BIST method is employed to ultimately produce a dock count proportional to the fall time of a capacitor, and in the case of differential capacitors a difference in count values. Each capacitor path has a controllable first DAC current or voltage source. A second DAC current or voltage source, later in the data path and isolated from the capacitor node(s), is controlled to offset the voltage contribution of the charged and discharging capacitor. A count is recorded, starting when a capacitor charging current is shut off, and ends (the count) when the voltage of the charged capacitor falls below a threshold. A difference in count between the two data path capacitors is calculated and reported. A state machine operates the sequencing and control of the BIST.

主权项

1. A method of testing an on-chip coupling capacitor of an integrated circuit having an amplifier for receiving signals through the on-chip coupling capacitor, said method comprising:
a) setting said coupling capacitor to a fully charged state using a first current or voltage source (first source); b) determining, using a second current or voltage source (second source) connected to an output of said amplifier on a data path isolated from said coupling capacitor, an offset voltage contribution of said coupling capacitor when in said charged state; c) storing said determined offset voltage value in a memory storage device; d) controlling a current or voltage supplied by said second source to a value sufficient to detect a coupling capacitor discharge state change at said isolated data path; e) initiating a discharging state of said coupling capacitor, and initiating a counter device to begin a counting; f) detecting when a signal representing said discharging state on said isolated data path has dropped below a threshold, and in response terminating counting by said counter device resulting in a count value; and g) evaluating a status of said on-chip coupling capacitor based on the count value.