21. That extent is defined by the operating frequency : as frequencies increase, the input impedance of the MOSFETs decreases. 22. As you may have seen, amplifiers are often marked with a minimum input impedance the speakers need to have. 23. The feedback also increases the input impedance of the amplifier when seen from the base, which can be advantageous. 24. As a result, the effective voltage across and the current through the impedance increase; the input impedance decreases. 25. A voltage buffer has a very high input impedance ( the opposition to current flow viewed from the load ). 26. DVM measurement accuracy is affected by many factors, including temperature, input impedance , and DVM power supply voltage variations. 27. The input impedance for high-impedance amplifiers ( such as vacuum tubes, field effect transistor amplifiers and pF ). 28. Because the input impedance of the common-gate amplifier is very low, the cascode amplifier often is used instead. 29. For example, a Tektronix P6139A input impedance starts falling above 10 kHz and is about 100 ohms at 100 MHz. 30. The distinguishing feature of Zobel networks is that the input impedance is fixed in the design independently of the transfer function.
