Pipelined ADC having a three-level DAC elements
First Claim
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1. An apparatus comprising:
- a logic circuit that includes;
a decoder that receives a control word and that generates a plurality of control signals from the control word; and
a plurality of predrivers that are each coupled to the decoder so as to receive at least one of the control signals; and
a plurality of three-state digital-to-analog converter (DAC) switches, wherein each three-state DAC is coupled to at least one of the predrivers, wherein each of the plurality of three-state DAC switches includes;
a current source;
a first transistor that is coupled to the current source and an associated predriver, wherein the associated predriver controls the first transistor;
a second transistor that is coupled to the current source and the associated predriver, wherein the associated predriver controls the second transistor; and
a third transistor that is coupled between the current source and ground and that is coupled to the associated predriver, wherein the associated predriver controls the third transistor.
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Abstract
In conventional pipelined analog-to-digital converters (ADCs), it is common to employ digital-to-analog converters (DACs) in the ADC stages that use two-state switches or segments. A problem with this arrangement is that for each DAC state there is a noise contribution from each DAC switch, resulting from its current source. Here, however, a DAC is employed that uses three-state DAC switches, which reduces the noise contributions from the DAC switches'"'"' current sources and reduces the amount of area used.
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Citations
15 Claims
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1. An apparatus comprising:
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a logic circuit that includes; a decoder that receives a control word and that generates a plurality of control signals from the control word; and a plurality of predrivers that are each coupled to the decoder so as to receive at least one of the control signals; and a plurality of three-state digital-to-analog converter (DAC) switches, wherein each three-state DAC is coupled to at least one of the predrivers, wherein each of the plurality of three-state DAC switches includes; a current source; a first transistor that is coupled to the current source and an associated predriver, wherein the associated predriver controls the first transistor; a second transistor that is coupled to the current source and the associated predriver, wherein the associated predriver controls the second transistor; and a third transistor that is coupled between the current source and ground and that is coupled to the associated predriver, wherein the associated predriver controls the third transistor. - View Dependent Claims (2)
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3. An apparatus comprising:
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a logic circuit that includes; a decoder that receives a control word and that generates a plurality of control signals from the control word; and a plurality of predrivers that are each coupled to the decoder so as to receive at least one of the control signals, wherein each predriver includes; a first current source; a second current source; a first cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; and a second cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; and a plurality of three-state DAC switches, wherein each three-state DAC is coupled to at least one of the predrivers. - View Dependent Claims (4, 5)
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6. An apparatus comprising:
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a digital output circuit; and a pipeline having a plurality of analog-to-digital converter (ADC) stages that are coupled in together in a sequence, wherein each ADC stage includes; a track-and-hold (T/H) circuit; a sub-ADC that is coupled to the T/H circuit and to the digital output circuit; a DAC that is coupled to the sub-ADC, wherein the DAC includes; a decoder that is coupled to the sub-ADC; a plurality of predrivers that are each coupled to the decoder; and a plurality of three-state DAC switches, wherein each three-state DAC is coupled to at least one of the predrivers, wherein each of the plurality of three-state DAC switches includes; a current source; a first transistor that is coupled to the current source and an associated predriver, wherein the associated predriver controls the first transistor; a second transistor that is coupled to the current source and the associated predriver, wherein the associated predriver controls the second transistor; and a third transistor that is coupled between the current source and ground and that is coupled to the associated predriver, wherein the associated predriver controls the third transistor; and a residue amplifier that is coupled to the DAC and the T/H circuit. - View Dependent Claims (7)
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8. An apparatus comprising:
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a digital output circuit; and a pipeline having a plurality of analog-to-digital converter (ADC) stages that are coupled in together in a sequence, wherein each ADC stage includes; a track-and-hold (T/H) circuit; a sub-ADC that is coupled to the T/H circuit and to the digital output circuit; a DAC that is coupled to the sub-ADC, wherein the DAC includes; a decoder that is coupled to the sub-ADC; a plurality of predrivers that are each coupled to the decoder, wherein each predriver includes; a first current source; a second current source; a first cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; and a second cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; a plurality of three-state DAC switches, wherein each three-state DAC is coupled to at least one of the predrivers; and a residue amplifier that is coupled to the DAC and the T/H circuit. - View Dependent Claims (9, 10, 11)
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12. An apparatus comprising:
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a digital output circuit that generates a digital output signal; a buffer that receives an analog input signal; a plurality of ADC stages that are coupled in together in a sequence, the first ADC stage of the sequence is coupled to the buffer, and wherein each ADC stage includes; a T/H circuit; a sub-ADC that is coupled to the T/H circuit and to the digital output circuit; a DAC that is coupled to the sub-ADC, wherein the DAC includes; a decoder that is coupled to the sub-ADC; a plurality of predrivers, wherein each predriver includes; a first current source; a second current source; a first cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; a second cascaded set of differential pairs of transistors that is coupled to first current source and to the decoder; and a plurality of three-state DAC switches, wherein each three-state DAC includes; a current source; a first transistor that is coupled to the current source and an associated predriver, wherein the associated predriver controls the first transistor; a second transistor that is coupled to the current source and the associated predriver, wherein the associated predriver controls the second transistor; and a third transistor that is coupled between the current source and ground and that is coupled to the associated predriver, wherein the associated predriver controls the third transistor; and a residue amplifier that is coupled to the first and second transistors from each three-state DAC switch and the T/H circuit; and an output ADC that is coupled to the last ADC stage of the sequence and the digital output circuit. - View Dependent Claims (13, 14, 15)
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Specification