Abstract: A method and apparatus is provided for monitoring performance of an processor to detect tampering and place the processor in a safe operating state that prevents unauthorized access to contents of the processor. In one example, the method and apparatus compares a measured value of an operating parameter (i.e., a temperature, supply voltage or clock signal) to predefined limits to identify an out of limits measured value. If an out of limits measured value is detected during a normal operating mode, the processor enters a reset mode, and if an out of limits measured value is detected during power up or reset, the processor in retained a reset mode.

Abstract: A method and apparatus is provided for monitoring performance of an processor to detect tampering and place the processor in a safe operating state that prevents unauthorized access to contents of the processor. In one example, the method and apparatus compares a measured value of an operating parameter (i.e., a temperature, supply voltage or clock signal) to predefined limits to identify an out of limits measured value. If an out of limits measured value is detected during a normal operating mode, the processor enters a reset mode, and if an out of limits measured value is detected during power up or reset, the processor in retained a reset mode.

Abstract: A monolithic integrated circuit for providing enhanced audio performance in personal computers. The monolithic circuit includes a wavetable synthesizer; a full function stereo coding and decoding circuit including analog-to-digital and digital-to-analog conversion; data compression, and mixing and muxing of analog signals; a local memory control module for interfacing with external memory; a game-MIDI port module; a system bus interface; and a control module for compatibility and circuit control functions.

Abstract: An active current steering semi-digital FIR filter for a digital-to-analog conversion circuit, which includes a shift register having a 1-bit digital input stream and a plurality of output taps, where each output tap provides a 1-bit signal which has a value of a logic 1 or a logic 0, and a plurality of current paths, where each path includes an active element, such as a transistor, having a relatively high output impedance, which is connected to a common current source, and to an op amp for current-to-voltage conversion. The relatively high output impedance of the active current steering element causes any error term resulting from offset at the op amp inputs to be minimized.

Abstract: A personal computer audio system is presented with a mechanism for digitally regulating the rate of voltage change of an audio output signal In one embodiment, the audio output signal from an integrated circuit is provided by means of a two-state audio amplifier. The first state of the amplifier is a high impedance state which exists prior to power-on and is maintained until an enable signal is asserted. When the enable signal is asserted, the amplifier drives the audio output signal line. Prior to the transition from the first to second states, a D/A converter is used to provide a ramp signal from the minimum voltage to the nominal operating voltage. The state transition is then initiated during the initial portion of the ramp signal.

Abstract: A digital wavetable audio synthesizer is described. The synthesizer can generate up to 32 high-quality audio digital signals or voices, including delay-based effects, at either a 44.1 KHz sample rate or at sample rates compatible with a prior art wavetable synthesizer. The synthesizer includes an address generator which has several modes of addressing wavetable data. The address generator's addressing rate controls the pitch of the synthesizer's output signal. The synthesizer performs a 10-bit interpolation, using the wavetable data addressed by the address generator, to interpolate additional data samples. When the address generator loops through a block of data, the signal path interpolates between the data at the end and start addresses of the block of data to prevent discontinuities in the generated signal. A synthesizer volume generator, which has several modes of controlling the volume, adds envelope, right offset, left offset, and effects volume to the data.

Abstract: Described herein is a fourth-order sigma-delta modulator which utilizes two second-order sigma-delta modulators connected together. Each second-order sigma-delta modulator is characterized as including integrators having a 1/2 sample period delay from input to output. A second-order sigma-delta modulator, including such integrators, exhibits a single sample period delay from input to output. A fourth-order sigma-delta modulator, which includes two such second-order sigma-delta modulators, exhibits a delay of two sample periods from input to output. The present sigma-delta modulator can be fabricated using switched capacitor circuitry to form an A/D convertor, and in another embodiment can be used as a digital noise shaper for a D/C convertor circuit. The 1/2 unit delay is implemented without requiring two D-flip flops in series, which results in a design and manufacturing advantage.

Abstract: A stereo audio CODEC, including means for performing D/A and A/D conversions, means for reducing digitally induced noise during attenuation/gain changes, data format conversion means, analog and digital filtering means, analog mixing means, on-chip 16-sample, 32-bit wide record and playback FIFOs, serial interface with external serial DSP, large local memory for supplementing on-chip record and playback FIFOs, control registers, register data bus and synthesizer DAC.

Abstract: An analog-to-digital conversion circuit is described which includes a front end sigma-delta modulator circuit, a multi-stage digital decimation filter circuit, and a digital compensation filter circuit. An overrange detect circuit is also provided.