The Digitizing Voltmeter Front End Module increases the accuracy (signal-to-noise ratio) of a small signal measurement by amplifying DUT signals at the test head.

Many mixed-signal devices have outputs that generate waveforms of very low amplitude. When these low amplitude signals are transmitted from the PTH to the test system via cables, a poor signal-to-noise (S/N) ratio can result. This is because noise is always introduced during transit through cabling and wiring, and small signals are often partially or completely obscured by this noise. The Digitizing Voltmeter Front End Module can increase the S/N ratio by processing analog waveforms prior to their transmission to the Digitizing Voltmeter (located in the test system).

A specific technique for increasing the S/N ratio is to increase the amplitude of the signal emerging from the DUT. The Digitizing Voltmeter Front End increases signal amplitude through the use of programmable gain stages.

In many cases, the signal cannot simply be amplified in its raw form. The signal may have some DC offset voltage that limits the amount of amplification that can be applied. The Digitizing Voltmeter Front End provides two methods to neutralize any unwanted DC offset: AC coupling and DC biasing.

In addition to amplifying the signal, the Digitizing Voltmeter Front End provides a filtering capability that allows only a specified range of frequencies to be amplified, while all others are attenuated.

Figure 5-1 shows a typical application example using the Digitizing Voltmeter Front End Module and the Waveform Generator Back End Module. A relatively large signal is generated by a Waveform Generator. The waveform is then attenuated by the Waveform Generator Back End Module. The DUT modifies the waveform. It is then amplified by the Digitizing Voltmeter Front End Module to maintain a large S/N ratio for an accurate reading at the Digitizing Voltmeter.