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Chapter 5 Theory of Operation
Amplitude Multiplier
5
Amplitude Multiplier
See “A1 Multiplier Schematic” on page 202.
Latching relay K1801 selects either the analog waveform, AWF, or the
digital waveform, DWF, for application to multiplier U1801. K1801 is
controlled by SET_AWF and SET_DWF from U306.
The amplitude multiplier provides approximately 10 dB of fine control to
the instrument’s output amplitude, interpolating between attenuator
steps. The multiplier also performs AM modulation.
U1801’s gain is determined by the differential voltage present at its “X”
input. This voltage, V_GAIN±, is generated in the Modulation circuitry
and typically ranges from 230 mV to 750 mV.
The waveform signal, as selected by K1801, is applied to U1801’s “Y1”
input and nominally ranges from –1 V to +1 V. The “Y2” input is driven
by V_NULL from the System DAC. V_NULL is set to correct for any
offset voltage present in the “Y1” input to ensure the multiplier’s output
offset remains constant as the gain voltage is changed.
The output of U1801 is buffered by U1802 to become the instrument’s
0 dB output (BUF_OUT).
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