| 摘要 |
A modified sign-magnitude DAC includes first internal DAC circuitry including a first number of bit switch circuits responsive to an input word including a sign bit and a digital data word. Each bit switch circuit is coupled to a corresponding current source transistor. Second internal DAC circuitry includes the same number of bit switch circuits responsive to the input word. Each bit switch circuit of the second internal DAC circuitry is coupled to a corresponding current source transistor. The same number of binarily weighted bit current determining resistor circuits corresponding to bits of the digital data word are connected to a reference voltage conductor. The emitter of the current source transistor of each bit switch circuit of the first internal DAC circuitry is coupled by a first gain balancing resistor to the corresponding bit current determining resistor. The emitters of the current source transistor of each bit switch circuit of the second internal DAC circuitry is connected by a second gain balancing resistor to the same corresponding bit current determining resistor. The sharing of the bit current determining resistor reduces the number required by half, and also reduces the physical size of each by half, since its resistance is halved for the same bit current magnitude.
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