Abstract: A method and apparatus for frequency modulating a PWM involves 1) generating a high frequency carrier signal much greater in frequency than the PWM signal; 2) modulating the high frequency signal to generate a spread spectrum carrier signal; and, 3) retiming a PWM signal with this high frequency SS carrier signal so that the binary transitions of the PWM signal are aligned with the frequency varying carrier signal. In another embodiment, a PWM oscillator is driven by a second, FM oscillator having spread spectrum characteristics. In another embodiment a PWM oscillator is driven and modulated by a counter/frequency divider comprised of modules.

Abstract: A method and apparatus for frequency modulating a PWM involves 1) generating a high frequency carrier signal much greater in frequency than the PWM signal; 2) modulating the high frequency signal to generate a spread spectrum carrier signal; and, 3) retiming a PWM signal with this high frequency SS carrier signal so that the binary transitions of the PWM signal are aligned with the frequency varying carrier signal. In another embodiment, a PWM oscillator is driven by a second, FM oscillator having spread spectrum characteristics. In another embodiment a PWM oscillator is driven and modulated by a counter/frequency divider comprised of modules.

Abstract: A method and apparatus for frequency modulating a PWM involves 1) generating a high frequency carrier signal much greater in frequency than the PWM signal; 2) modulating the high frequency signal to generate a spread spectrum carrier signal; and, 3) retiming a PWM signal with this high frequency SS carrier signal so that the binary transitions of the PWM signal are aligned with the frequency varying carrier signal. In another embodiment, a PWM oscillator is driven by a second, FM oscillator having spread spectrum characteristics. In another embodiment a PWM oscillator is driven and modulated by a counter/frequency divider comprised of modules.

Abstract: A method and device to emulate impedances includes a pair of impedances connected in series between two circuit nodes, the impedances forming a voltage divider having at its midpoint a reference voltage VX. An OP AMP includes a positive input connected to the VX—node and the negative input connected to the output thereof in a direct feedback loop. The OP AMP output is also connected to a load impedance that is connected either one of the nodes. A transistor may be interposed between the load impedance and the circuit node. The OP AMP may be provided with a negative gain to emulate an inductor. The voltage divider may be variable to emulate a variable impedance.

Abstract: A dual function circuit for providing an output voltage to a transimpedance amplifier is disclosed. The dual function circuit can be selected between functioning as a current to voltage conversion circuit connected to a photodiode and as a testing circuit for testing the transimpedance amplifier without exposing light to the photodiode. The dual function circuit comprises two current mirror pairs to ensure that a substantially similar dc bias current is applied to the two driving transistors. In addition, by applying an input testing voltage to the two driving transistors in a common gate/base design, the output of the testing circuit has wide band frequency response. No switching is required to select between the test mode and the normal mode.

Abstract: A method and device to emulate impedances includes a pair of impedances connected in series between a supply voltage and ground, the impedances forming a voltage divider having at its midpoint a reference voltage Vx. An OP AMP includes a positive input connected to the Vx node and the negative input connected to the output thereof in a direct feedback loop. The OP AMP output is also connected to a load impedance that is connected either to the supply voltage or ground. The unity gain OP AMP forces the output voltage thereof to follow the input voltage Vx, whereby the output voltage behaves as if it were created by a virtual impedance. By proper choice of components and values, the virtual impedance may comprise a large capacitor, and the remaining impedances may comprise resistance and small capacitance, both of which, together with the OP AMP, are easily integrated in a small die area.

Abstract: An electrostatic discharge (ESD) protection circuit includes circuitry for providing protection against ESD events which occur either within an ESD pad ring (intra-ring) or between different ESD pad rings (inter-ring). Self-triggering voltage clamp circuits or back-to-back diode circuits can be used to properly interconnect the positive polarity rails and the negative polarity rails of the ESD pad rings. Self-triggering voltage clamp circuits are advantageous in that they provide improved ac signal isolation (i.e. reduced noise coupling between the ESD pad rings, and thus reduced noise coupling from the digital I/O pads to the analog I/O pads).

Abstract: A compensated, bias-dependent signal filtration and amplification circuit includes a low-pass RC filter with a bias-dependent frequency response caused by the use of MOS transistors connected as capacitors with bias-dependent capacitances. A dc current source is used, in cooperation with the resistors of the RC filter, to generate a fixed bias for the capacitor-connected MOS transistors and thereby eliminate the bias dependencies of the capacitances. Following amplification of the filtered signal, another dc current is subtracted out from the amplified output signal so as to eliminate any residual dc signal components due to the input compensation dc bias signal, thereby leaving only the amplified filtered ac signal components.