| 摘要 |
A transformer (90) includes taps (96a, 96b, 96c) by which electrical contact can be made to a winding (90) of the transformer (90) at locations along its length between its end terminals. A first section (90a) of the winding (90) has a first resistance R1 (R). A second section (90a+90b) of the winding (90) has a second resistance R2 (R+3R). One or both of the first (90a) and second (90a+90b) sections can be a multilayer section. The sections are configured so that one of the ratio R1:R2 (1:4) and the ratio R2:R1 (4:1) is substantially identical to the ratio 1:n (1:4) of the windings (90a, 90a+90b). A first switch (94) permits contact to be made selectively to a selected one of the taps (96a, 96b, 96c). An amplifier (98) has an inverting (-) input terminal, a non-inverting (+) input terminal and an output terminal. One (+) of the + and - input terminals is coupled to one of the terminals (end terminal of winding 90a) of the winding (90). In one embodiment (without switch 92, and with the configuration illustrated in FIG. 8), the other (-) of the + and - input terminals is coupled to the output terminal of the amplifier (98). In another embodiment, a second switch (92) also permits contact to be made selectively to a selected one of the taps (96a, 96b, 96c). The other (-) of the + and - input terminals is coupled to the other terminal (end terminal of winding 90c) of the winding (90). The output terminal of the amplifier (98) is coupled to the first switch (94) so that selectively making contact with one of the taps (96a, 96<highlight><i
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