Input impedance
The input resistance (also outdoor resistance, load resistance, terminating resistor, load resistor) located at the entrance of an electrical device or component and loads the source device to this input provides its tension.
The feeding device has a source resistance ( source impedance ), which is usually much smaller than the input resistance of the powered device when the voltage adjustment.
For DC voltages, but especially for changes and signal voltages, and especially in high-frequency power adjustment applies to that output resistance and input resistance have the same value - impedance matching.
With terminating resistor (also dummy load, dummy load or shortly called completion ) will ( mostly in the form of a plug ) denotes a high-frequency -compatible resistor and the technical execution of, for example, for measurement purposes or to avoid reflections as a load to a signal source or line is connected. For the test of transmitters terminating resistors with a correspondingly high power is required ("artificial antennas "). Such termination resistors must be constructed in a particularly low inductance, therefore only uncoiled film resistors or ground resistors are used.
- An oscilloscope is typically the input resistance of 1 M to weight the measurement point (<< 1 M ) only slightly. By connecting a probe of the input impedance can be increased to 10 M or more; simultaneously, thus avoiding the influence of the measuring line.
- Voltmeter and multimeters have the same reason as high input resistances; latter usually have an input resistance of 10 M.
- (Eg, LAN, wireless transmitter and receiver ) fed to a radio-frequency device a signal via cable, this must be one that matches the cable impedance input resistance (often 50 Ω ) have to avoid pulse reflections (see custom line ). The input impedance of antenna is called a base impedance.
- Input resistors are always " passive " while output resistances are mainly "active", as can be clearly seen here in the picture. A passive input can not be " short "; shorted sources only serve as a model. The internal resistance Ri, output resistance and source resistance may be passive, such as damping and impedance matching elements.
- Often the load, external or input resistance with and referred to the source, internal or output resistor, resulting in more misunderstandings because external resistance (load ) Output resistance (source) can not be. The terms and are to be avoided because only the outer, load or input resistance can be.
- In Transfer Consoles IRT Issue 3 /5 ( 1989) ( input impedance ) has to be of normal level inputs within the entire frequency range (40 Hz to 15 kHz) greater than 5 k. At microphone amplifier inputs ( input impedance ) is to be greater than 1 kOhm. The deviations are to remain in the entire frequency range below 20 %.
- An amplifier should be as low as possible source impedance (< 0.1 Ω ) have to cut out the speaker as well as possible with a nominal load impedance of eg 4 or 8 Ω; see damping factor.
With alternating the input resistance is often a complex resistance which includes inductive and capacitive components. Complex resistors is called impedance.
Input and output resistors must not necessarily be represented by real resistors, but can from the behavior (impedance ) result of a complex active or passive circuit.
In op-amp outputs of the terminator is often determined by a passive resistance - the operational amplifier itself usually has a too low source resistance or may not be too heavily loaded to function as calculated.