Digital-to-analog converter having enhanced current steering and associated method
First Claim
1. A digital-to-analog converter comprising:
- digital input means for receiving a plurality of digital input signals;
at least one output current summing bus; and
a plurality of current cells connected to said digital input means and said at least one output current summing bus, at least one of said current cells comprisinga current source,a pair of bipolar current switching transistors connected to said current source and said at least one output current summing bus in a current steering configuration so that one transistor is off while the other transistor is on, said pair of bipolar current switching transistors having a proportion of current steering based upon a difference in base-emitter voltages and also based upon a thermal voltage, andtemperature compensated control means for controlling the difference in base-emitter voltages of said bipolar current switching transistors based upon a temperature dependent bias voltage to compensate for the thermal voltage.
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Abstract
A digital-to-analog converter includes a plurality of current cells, at least one cell in one embodiment including a pair of bipolar current switching transistors connected to a current source and a current summing bus in a current steering configuration so that one transistor is off while the other transistor is on. A temperature compensated control circuit is included for controlling the difference in base-emitter voltages of the bipolar current switching transistors based upon a temperature dependent bias voltage to compensate for a thermal voltage of the bipolar transistors. The temperature compensated control circuit preferably comprises a proportional to absolute temperature (PTAT) current source, and a steering pair of transistors connected to the PTAT current source and the pair of bipolar current switching transistors. The PTAT current source and steering transistors effectively bias the current switching transistors to account for the thermal voltage of the bipolar transistors. Method aspects of the invention are also disclosed.
100 Citations
30 Claims
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1. A digital-to-analog converter comprising:
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digital input means for receiving a plurality of digital input signals; at least one output current summing bus; and a plurality of current cells connected to said digital input means and said at least one output current summing bus, at least one of said current cells comprising a current source, a pair of bipolar current switching transistors connected to said current source and said at least one output current summing bus in a current steering configuration so that one transistor is off while the other transistor is on, said pair of bipolar current switching transistors having a proportion of current steering based upon a difference in base-emitter voltages and also based upon a thermal voltage, and temperature compensated control means for controlling the difference in base-emitter voltages of said bipolar current switching transistors based upon a temperature dependent bias voltage to compensate for the thermal voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A digital-to-analog converter comprising:
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digital input means for accepting a plurality of digital input signals; at least one output current summing bus; and a plurality of current cells connected to said digital input means and said at least one output current summing bus, at least one of said current cells comprising a current source, a pair of bipolar current switching transistors connected to said current source and said at least one output current summing bus in a current steering configuration so that one transistor is off while the other transistor is on, said pair of bipolar current switching transistors having a proportion of current steering based upon a difference in base-emitter voltages and also based upon a thermal voltage, a proportional to absolute temperature (PTAT) source, and a pair of steering transistors connected to said PTAT source and said pair of bipolar current switching transistors for controlling the difference in base-emitter voltages of said bipolar current switching transistors based upon the PTAT source to provide a predetermined proportion of current steering over a relatively wide temperature range to thereby compensate for the thermal voltage. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22)
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23. A current cell comprising:
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a current source; a pair of bipolar current switching transistors connected in a current steering configuration so that one transistor is off while the other transistor is on, said pair of bipolar current switching transistors having a proportion of current steering based upon a difference in base-emitter voltages and also based upon a thermally dependent voltage; and temperature compensated control means for controlling the difference in base-emitter voltages of said bipolar current switching transistors based upon a temperature dependent bias voltage to compensate for the thermally dependent voltage, said temperature compensated control means comprising a proportional to absolute temperature (PTAT) current source, and a pair of steering transistors and associated bias resistors connected to said PTAT current source and said pair of bipolar current switching transistors for controlling the difference in base-emitter voltages of said bipolar current switching transistors based upon absolute temperature. - View Dependent Claims (24, 25)
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26. A method of steering current in a current cell of a plurality of such current cells connected to an output current summing bus of a digital-to-analog converter, each current cell comprising a pair of current switching transistors connected together in a current steering configuration so that one transistor is off while the other transistor is on, the pair of current switching transistors having a proportion of current steering based upon a difference in transistor control voltages and also based upon a thermally dependent voltage, the method comprising the steps of:
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receiving at least one digital input signal; supplying a current to the pair of current switching transistors for steering based upon the digital input signal; and controlling the difference in transistor control voltages of the current switching transistors based upon a temperature dependent bias voltage to compensate for the thermally dependent voltage. - View Dependent Claims (27, 28, 29, 30)
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Specification