Apparatus and method for common-mode regulation in a switched capacitor circuit

#The present invention relates generally to switched capacitor circuits. More particularly, the present invention relates to an apparatus and method that reduces the requirements and number of voltage references that are necessary for proper operation in a switched capacitor circuit while maintaining an optimized common-mode input voltage.

#A one-bit over-sampling analog-to-digital converter (600) is depicted in FIG. 6. This type of analog-to-digital converter (ADC) is often referred to as a first order delta-signal (ΔΣ) modulator. As shown in the figure, the first order ΔΣ-modulator (600) includes a summer (601), an integrator (602), a 1-bit ADC (603) a digital low pass filter (604), and a 1-bit digital-to-analog converter (605). The first order ΔΣ-modulator (600) receives an analog signal and produces an N-bit digital code output.

#In operation, an analog signal and an output of 1-bit digital-to-analog converter (DAC) 605 are fed into summer 601. The summer (601) provides an output that corresponds to the difference between the analog input signal and the output of DAC 605. The integrator (602) provides an integration signal in response the difference signal. The 1-bit ADC (603) produces a digital bit by converting by comparing the integration signal to a predetermined threshold level (i.e., mid-supply level). This digital bit is fed into the 1-bit DAC, which produces an analog voltage that corresponds to one of two voltages (i.e., +VREF and -VREF). Digital low pass filter (LPF) 604 receives the digital bit from the 1-bit ADC (603) and produces an N-bit digital code output.

#FIG. 1 is a schematic diagram illustrating an exemplary operating environment;

#FIG. 2 is a schematic diagram illustrating a first embodiment; and

#FIG. 3 is a schematic diagram illustrating the sampling mode operation of the embodiment shown in FIG. 2;

#Throughout the specification, and in the claims, the term “connected” means a direct electrical connection between the things that are connected, without any intermediary devices. The term “coupled” means either a direct electrical connection between the things that are connected, or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means one or more passive and/or active components that are arranged to cooperate with one another to provide a desired function. The term “signal” means at least one current signal, voltage signal, electromagnetic wave signal, or data signal. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on”.

#The present invention generally relates to switched capacitor circuits. Switched capacitor circuits are often used in delta-sigma modulator (ΔΣ-modulator) type analog-to-digital converters (ADC) as integrator circuits. The present invention allows a switched capacitor integrator circuit to operate with a minimum number of reference voltages such that the overall system design is simplified. Costs are reduced since fewer reference circuits are required by the system. Also, the common-mode input voltage of the amplifiers in the improved design allow the amplifiers to work on at very low power supply levels on the order of 1.8V.

#The operating environment for the switched capacitor integrator circuit is described below with reference to FIG. 1.