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US RE38,083 E1Granted
Rail-to-rail DAC drive circuit
AssigneeAnalog Devices, Inc.
InventorJames J. Ashe
Life of this patent
Estimating the term…
Abstract
A voltage mode digital-to-analog converter (DAC) with an output buffer operational amplifier is provided with a rail-to-rail output voltage capability by reducing the DAC's output voltage swing to a range that is within the amplifier's permissible input signal range, and connecting the amplifier in a multiplier configuration to produce a corresponding multiplication of its input signal. The DAC output reduction is preferably achieved by delivering an n-bit input digital signal to an n+m bit DAC, and holding the DAC's m most significant bits OFF. The m most significant bits are dummy bits that are impedance matched with the DAC, while the amplifier is an operational amplifier with a feedback circuit that is also impedance matched to the DAC.
Claims42
A digital-to-analog converter (DAC) drive circuit, comprising:
- a pair of voltage reference nodes for supplying different reference voltage levels,
- a DAC that is connected to receive an input digital signal, and to be supplied directly by both of said voltage reference nodes at the full reference voltage levels, said DAC having multiple bit positions and including m dummy bits in the most significant of said bit positions, said DAC being connected to receive an n-bit input digital signal and, including said dummy bits, having n+m bits, said dummy bits being continually held OFF, and
- an amplifier that is connected to receive an analog input from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the full range between said reference voltage levels, said dummy bits reducing the DAC's analog output swing to a range that is within the amplifier's permissible input signal range,
- said amplifier providing its output with a greater than unity amplification.
1 more element
A digital-to-analog converter (DAC) drive circuit, comprising:
- high and low reference nodes for supplying high and low reference voltage levels,
- a DAC that is connected to receive an input digital signal and to produce a corresponding analog output signal with a voltage swing that is limited to the voltage range between said high and low reference voltage levels, divided by a factor D, and
- an operational amplifier supplied with power from said high and low voltage reference nodes, said amplifier having a permissible input signal range that is less than the difference between said high and low reference voltages, said amplifier being connected to amplify its input by said factor D, and thereby produce an amplified output that can swing substantially through the full range between said high and low reference voltage, said amplifier having its non-inverting input connected to receive the DAC output and its inverting input connected in a feedback circuit with its output, said feedback circuit having an input impedance that matches the output impedance of said DAC.
A digital-to-analog converter (DAC) drive circuit, comprising:
- a DAC that is connected to receive an input digital signal and to produce a corresponding analog output signal with a predetermined swing range,
- an operational amplifier that is connected to receive an analog input from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the DAC's analog output signal swing range, and
- a divider that is connected to reduce the DAC's analog output swing to a range that is within the amplifier's permissible input signal range,
- said amplifier receiving its input from said DAC through said divider and providing its output with a greater than unity amplification, said amplifier having its non-inverting input connected to receive the DAC output and its inverting input connected in a feedback circuit with its output, said feedback circuit having an input impedance that matches the output impedance of said DAC.
1 more element
A digital-to-analog converter (DAC) drive circuit, comprising:
- a pair of voltage reference nodes for supplying different reference voltage levels,
- a DAC that is connected to receive an input digital signal, and to be supplied by said voltage reference nodes,
- an amplifier that is connected to receive an analog input from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the full range between said reference voltage levels, and
- a divider that is connected to reduce the DAC's analog output swing to a range that is within the amplifier's permissible input signal range,
- said amplifier receiving its input from said DAC through said divider, and providing its output with a greater than unity amplification,
- said divider comprising an attenuation network that is impedance matched to the DAC, said attenuation network implemented as m dummy bits in the most significant bit positions of said DAC, said DAC being connected to receive an n-bit input digital signal and, including said dummy bits, having n+m bits, said dummy bits being continually held OFF,
- said DAC comprising an R-2R ladder and an associated switching network for connecting each of its n least significant bits (LSBs) respectively to one or the other of said voltage reference nodes, said switching network including respective pairs of switches connected in circuit with an 2R resistor of each of said n LSBs, with one switch of each pair connecting its respective 2R resistor to one of said voltage reference nodes and the other switch of each pair connecting its respective 2R resistor to the other of said voltage reference nodes, and a control network that turns one switch of each pair ON and the other switch of each pair OFF in accordance with said input digital signal, said dummy bits each including a single switch connecting an associated 2R dummy bit resistor to one of said voltage reference nodes that corresponds to an OFF bit output, with said single switch held ON for all digital inputs,
- said amplifier comprising an operational amplifier having its non-inverting input connected to receive the DAC output and its inverting input connected in a feedback circuit with its output, said feedback circuit having an input impedance that matches the output impedance of said DAC.
5 more elements
A digital-to-analog converter (DAC) drive circuit, comprising:
- a pair of voltage reference nodes for supplying different reference voltage levels,
- a DAC that is connected to receive an input digital signal, and to be supplied by said voltage reference nodes,
- an amplifier that is connected to receive a analog input from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the full range between said reference voltage levels, and
- a divider that is connected to reduce the DAC's analog output swing to a range that is within the amplifier's permissible input signal range,
- said amplifier receiving its input from said DAC through said divider and providing its output with a greater than unity amplification, said amplifier comprising an operational amplifier having its non-inverting input connected to receive the DAC output and its inverting input connected in a feedback circuit with its output, said feedback circuit having an input impedance that matches the output impedance of said DAC.
2 more elements
A digital-to-analog converter (DAC) drive circuit, comprising:
- a pair of voltage reference nodes for supplying different reference voltage levels,
- a DAC that includes a conversion section connected to receive a digital input signal and convert the digital signal to an analog output signal, and an attenuation section, said DAC connected to be supplied directly by both of said voltage reference nodes at the full reference voltage levels, and
- an amplifier having an input that is connected to receive the analog output from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the full range between said reference voltage levels, and a greater than unity amplification;
- said attenuation section connected to said DAC conversion section to reduce the DAC's analog output swing to a range that is within the amplifier's permissible input signal range.
1 more element
A digital-to-analog converter (DAC) drive circuit, comprising:
- a pair of voltage reference nodes for supplying different reference voltage levels,
- a DAC that is connected to receive an input digital signal, and to be supplied directly by both of said voltage reference nodes at the full reference voltage levels, and
- an amplifier that is connected to receive an analog input from said DAC and to provide a drive output, said amplifier having a permissible input signal range that is less than the full range between said reference voltage levels,
- said DAC including an attenuation portion that reduces the DAC's analog output swing to a range that is within the amplifier's permissible input signal range, said amplifier providing its output with a greater than unity amplification.
1 more element
A digital-to-analog converter (DAC) drive circuit, comprising:
- high and low reference nodes for supplying high and low reference voltage levels,
- a DAC that is connected to receive the full voltage differential between said reference nodes and an input digital signal, and to produce a corresponding analog output signal with a voltage swing that is limited to the voltage range between said high and low reference voltage levels divided by a factor D, and
- an operational amplifier supplied with power from said high and low voltage reference nodes, said amplifier having a permissible input signal range that is less than the difference between said high and low reference voltages, said amplifier connected to amplify its input by said factor D, and thereby produce an amplified output that can swing substantially through th e full range between said high and low reference voltage levels.
Dependencies are inferred from the claim text.