Distributed gain line driver amplifier including improved linearity
First Claim
1. A line driver amplifier comprising:
- at least one adaptive gain amplifier; and
at least one distributed gain amplifier connected in parallel with said adaptive gain amplifier, said at least one distributed gain amplifier includes at least a first distributed gain amplifier stage including a first plurality of auxiliary amplifiers, each of said auxiliary amplifiers in said first plurality of auxiliary amplifiers having an input and an output and including a prescribed offset voltage level, and a first plurality of output transistors, each of said output transistors in said first plurality of output transistors being in a prescribed circuit relationship with the output of a respective one of said first plurality of auxiliary amplifiers forming a first plurality of auxiliary amplifier-output transistor pairs that are connected in parallel circuit relationship with each other, wherein each of said output transistors in said first plurality of output transistors is in an OFF state until an input signal supplied to the inputs of said first plurality of auxiliary amplifiers has a signal magnitude equal to or greater than the offset voltage level of the respective auxiliary amplifier in circuit relationship to said respective output transistor, whereby abrupt changes in a transfer function of said line driver amplifier are smoothed out.
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Abstract
Improved linearity in a line driver amplifier is realized by employing one or more amplifier sections each including an adaptive gain amplifier connected in parallel with a distributed gain amplifier. In an embodiment of the invention, first and second amplifier sections are connected in circuit relationship to an input and an output of the line driver amplifier to form a symmetrical amplifier configuration. In a specific embodiment of the invention, the adaptive gain amplifiers in each amplifier section are class AB type amplifiers and the distributed gain amplifiers in each amplifier section are class B amplifiers. Specifically, each of the distributed gain class B amplifiers each include a plurality of output transistors and a corresponding plurality of auxiliary amplifiers. The output transistor and auxiliary amplifier pairs are connected in parallel. Each of the auxiliary amplifiers includes a built in voltage offset, beginning with an auxiliary amplifier having the smallest voltage offset to the auxiliary amplifier having the largest offset. The individual auxiliary amplifiers maintain their corresponding output transistors in an OFF state so long as the overall amplifier input signal has a magnitude less than the auxiliary amplifier offset voltage level. When the input signal magnitude level is equal to or greater than the offset level of an auxiliary amplifier, that auxiliary amplifier turns its corresponding output transistor to an ON state. Thus, for lower magnitude input signals fewer than all of the output transistors are in an ON state, while for maximum magnitude input signals all of the output transistors are in an ON state. Use of the auxiliary amplifier-output transistor pairs allows use of smaller size transistors, each of which has a lower output current than an equivalent single output transistor. Since all of the output transistors in each amplifier stage are connected in parallel, the amplifier output current is the sum of the currents passing through the ON output transistors. Moreover, the adaptive gain class AB amplifier'"'"'s gain varies as a function of input signal such that for larger input signals there is more gain and, consequently, less distortion. By employing the adaptive gain amplifiers and distributed gain amplifiers the line driver amplifier open loop gain characteristic is much smoother resulting in increased linearity.
17 Citations
44 Claims
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1. A line driver amplifier comprising:
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at least one adaptive gain amplifier; and
at least one distributed gain amplifier connected in parallel with said adaptive gain amplifier, said at least one distributed gain amplifier includes at least a first distributed gain amplifier stage including a first plurality of auxiliary amplifiers, each of said auxiliary amplifiers in said first plurality of auxiliary amplifiers having an input and an output and including a prescribed offset voltage level, and a first plurality of output transistors, each of said output transistors in said first plurality of output transistors being in a prescribed circuit relationship with the output of a respective one of said first plurality of auxiliary amplifiers forming a first plurality of auxiliary amplifier-output transistor pairs that are connected in parallel circuit relationship with each other, wherein each of said output transistors in said first plurality of output transistors is in an OFF state until an input signal supplied to the inputs of said first plurality of auxiliary amplifiers has a signal magnitude equal to or greater than the offset voltage level of the respective auxiliary amplifier in circuit relationship to said respective output transistor, whereby abrupt changes in a transfer function of said line driver amplifier are smoothed out. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A line driver amplifier comprising:
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an adaptive gain amplifier including a first adaptive gain amplifier stage having a first adaptive gain stage and a first associated output transistor and a second adaptive gain amplifier stage having a second adaptive gain stage and a second associated output transistor; and
a distributed gain amplifier including a first distributed gain amplifier stage having a first distributed gain stage and a first associated distributed output transistor and a second distributed gain amplifier stage having a second distributed gain stage and a second associated distributed output transistor, said first adaptive gain amplifier stage being connected in parallel with said first distributed gain amplifier stage, and said second adaptive gain amplifier stage being connected in parallel with said second distributed gain amplifier stage, each of said first and second distributed amplifier stages including a first and a second plurality of auxiliary amplifiers, respectively, each of said auxiliary amplifiers having an input and an output and including a prescribed offset voltage level, and each of said first and second distributed output transistors being in a prescribed circuit relationship with the output of a respective one of said first and second plurality of auxiliary amplifiers forming first and second pluralities of auxiliary amplifier-output transistor pairs that are connected in parallel circuit relationship with each other, wherein each of said distributed output transistors is in an OFF state until an input signal supplied to the inputs of said auxiliary amplifiers has a signal magnitude equal to or greater than the offset voltage level of the respective auxiliary amplifier in circuit relationship to said respective one of said distributed output transistors, whereby linearity of said line driver amplifier is improved and distortion is decreased. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44)
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Specification