1. Field of the Invention
The present invention relates to a frequency characteristic measuring circuit incorporated in a semiconductor integrated circuit for high-speed signal transmission having an input/output (I/O) circuit, and in particular, relates to a frequency characteristic measuring circuit used for excluding shipment of defective semiconductor integrated circuits by detecting defective frequency characteristics of the semiconductor integrated circuits when the semiconductor integrated circuits are in volume production.
2. Description of the Related Art
Conventionally, in order to measure frequency characteristics of a transmitting circuit or a receiving circuit embedded in a semiconductor integrated circuit (hereinafter, referred to as an LSI) for high-speed signal transmission, a signal of a high-frequency signal generator is input into the receiving circuit and output of the receiving circuit is routed out of the LSI using special I/O such as low-voltage differential signaling (LVDS) to thereby measure the output by a measuring apparatus outside the LSI. In this case, frequency characteristics required of the special I/O exceed those of a measuring object.
However, it is very difficult to extract a signal of frequencies in the GHz band or higher from the LSI with reliability due to an influence of package capacitance, printed circuit board (PCB) capacitance, or input capacitance of a measuring apparatus. Even if a signal of frequencies in the GHz band or higher can be extracted from the LSI with reliability, a measurement environment and measuring equipment will be very expensive in that case, requiring new investment in equipment for volume production of LSIs.
Incidentally, Jpn. Pat. Appln. KOKAI Publication No. 11-202032 discloses a method of determining a mounting state of an inspected circuit on a substrate by connecting an oscillator generating a signal of any frequency to an inspection terminal, providing a measuring apparatus for measuring frequency characteristics of an analog signal on the substrate, causing the oscillator to digitally output a signal of any frequency from the inspection terminal to an inspected terminal to measure frequency characteristics of the analog signal by the measuring apparatus, and comparing the measured measurement result with determination values.