Method and apparatus to generate mixed signal test stimulus

A circuit tester comprising:

• a memory operable to store a digital signal comprising a stream of one-bit samples that were generated using sigma delta modulation;
• a timing and formatting circuit for receiving the digital signal from the memory and controlling the timing of the digital signal for processing;
• a signal modification circuit coupled to the timing and formatting circuitry and operable to receive the digital signal from the timing and formatting circuitry and to introduce a DC level shift to the digital signal, wherein the output of the signal modification circuit can be filtered to produce an analog signal;
• a filter coupled to the signal modification circuit and operable to receive the digital signal from the signal modification circuit and to filter the digital signal to generate an analog signal;
• and
• a selector circuit coupled to the signal modification circuit and the filter, the selector circuit operable to receive the digital signal from the signal modification circuit and the analog signal from the filter and to select one signal as an output signal.

A method of generating signals comprising:

• storing a digital signal in a memory, the digital signal comprising a precomputed noise-shaped digital representation of an analog signal, the digital signal further comprising a series of one bit samples that were generated using sigma delta modulation;
• outputting the digital signal from the memory;
• filtering the digital signal using a filter to generate an analog signal;
• selecting between an output of the memory, directly or indirectly, and the output of the filter;
• and
• transmitting the selected signal as an output signal.