| 摘要 |
An overvoltage and transient protection circuit with extended bandwidth is provided for the protection of a low voltage test signal path (210) such as a test signal path in a multimeter. The disclosed circuit maintains the integrity of a test signal (TS) (114) transmitted by the test signal path (210) by minimizing the effect that unwanted capacitive coupling would otherwise have on the frequency transmission capability of the circuit. During normal operation of the circuit, a test signal path isolation circuit (218) is held between the test signal (TS) (114) and an equivalent buffered guard signal (GS) 227. Held between these equivalent values (TS=GS), no (or minimal) current will be generated in the components of the test signal path isolation circuit (218) as a result of parasitic capacitance. The guard signal (65) (227) is used with guard traces (412) and guard planes (414) to isolate other parts of the test signal path in much the same way. During an overvoltage condition, the test signal path isolation circuit (218) conducts the current resulting from the overvoltage to a clamp circuit (222) that conducts to a voltage limiting circuit. The test signal path (210) may also include a frequency compensated protective resistance (320) that may be relatively high in value.
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