Integrated digitally controlled linear-in-decibels attenuator
AssigneeNational Semiconductor Corporation
InventorHon Kin Chiu
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Abstract
An integrated digitally controlled linear-in-decibels attenuator circuit in which one or more sets of selection switches establish a desired attenuation by selectively connecting the input signal electrode to one or more corresponding resistive ladder networks connected in series, thereby providing a substantially more constant signal attenuation value over a wider frequency bandwidth. With a single resistive ladder network, attenuation control is achieved using a thermometer switching code. With multiple resistive ladder networks, coarse and fine attenuation control can be achieved using thermometer and bubble switching codes, respectively.
Claims12
An apparatus including an integrated digitally controlled linear-in-decibels attenuator circuit, comprising:
- first switched resistance circuitry responsive to a first plurality of digital control signals by attenuating an input signal to provide a first attenuated signal having a magnitude substantially in accordance with one of a first plurality of attenuation values mutually separated by a first attenuation step substantially in accordance with a thermometer code;
- and
- second switched resistance circuitry coupled to said first switched resistance circuitry and responsive to a second plurality of digital control signals by attenuating said first attenuated signal to provide a second attenuated signal having a magnitude substantially in accordance with one of a second plurality of attenuation values mutually separated by a second attenuation step substantially in accordance with a bubble code, wherein said second attenuation step is smaller than said first attenuation step;
- wherein a ratio of said second attenuated signal and said input signal is one of a plurality of ratio values mutually separated by linear-in-decibels steps.
A method for attenuating a signal in a linear-in-decibels manner in accordance with a plurality of digital control signals, comprising:
- attenuating an input signal in accordance with a first plurality of digital control signals to provide a first attenuated signal having a magnitude substantially in accordance with one of a first plurality of attenuation values mutually separated by a first attenuation step substantially in accordance with a thermometer code;
- and
- attenuating said first attenuated signal in accordance with a second plurality of digital control signals to provide a second attenuated signal having a magnitude substantially in accordance with one of a second plurality of attenuation values mutually separated by a second attenuation step substantially in accordance with a bubble code, wherein said second attenuation step is smaller than said first attenuation step;
- wherein a ratio of said second attenuated signal and said input signal is one of a plurality of ratio values mutually separated by linear-in-decibels steps.
Dependencies are inferred from the claim text.