Importance

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Abstract

An integrated circuit, including a resistor having multiple, series-connected resistor segments formed over multiple tubs of semiconductor material of a first polarity in a semiconductor substrate of the opposite polarity. The resistor is implemented with multiple bootstrapping in the sense that all tubs are coupled to a node of the circuit whose potential changes, in response to a changing input signal, in a direction so as to pull the potential at one end of the resistor in a desired direction. Each resistor segment can be formed over a different one of the tubs, or there are more segments than tubs (e.g., more than one segment formed over one of the tubs or at least one segment having no tub under it). In preferred embodiments, the circuit is a high-speed cascode amplifier (or other amplifier), the resistor is a gain-setting resistor coupled to the top rail, and the tubs are coupled to the amplifier's output. Implementing the resistor in accordance with the invention results in faster amplifier response (to a rapidly changing input) and (if the resistor has a field oxide layer between the resistor segments and the underlying semiconductor material) reduced dependence of the response time on the field oxide layer thickness. In a preferred embodiment, the resistor comprises ten segments of polysilicon connected in series over three tubs of N-type semiconductor material in a P-type semiconductor substrate (with a field oxide layer separating each tub from the segment or segments overlying it).

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First Claim