The measurement of Class-D and other PWM or Delta-Sigma digital modulator type output stage amplifiers often presents a problem due to high frequency switching noise components. These high frequency componenets can obstruct the measurement of in-band typical 20-20kHz measurements.

Many of these amplifiers have limited high frequency filtering of their own, and many analyzers or other measuring instrumentation have no or insufficient filtering to remove the passband effects of these strong high frequency out-of-band components. The LF280™ offers a steep 80kHz 8th order passive lowpass filter to remove these unwanted high frequency components and enable accurate in-band amplifier response measurements.

The LF280™ is constructed entirely of the latest high linearity ultra high permeability gapped Ferrite inductors and Polypropylene capacitors for the ultimate in stability, high frequency performance, reduction of high frequency loss, and maximum linearity. The LF280™ utilizes a unique topology of identical component values to greatly reduce component sensitivity and produce a highly stable response with maximum passband flatness and outstanding stopband attenuation.

A common problem with any passive filter is loading by the external cable capacitance or analyzer/meter input circuitry which can alter the passband response. The LF280™ provides a precision R2R ladder attenuator which effectively removes the effects of external device loading, and provides a constant low output impedance regardless of the attenuation selected.

For attenuation levels of -12dB or lower the effects of any external device loading are effectively eliminated. An additional advantage of the precision attenuator is to reduce signal levels fed to other measuring devices which may not be capable of handling the very large signals produced from high power amplifiers.