98
5
The 14–bit waveform DAC is loaded with data from the Synthesis IC.
The output is then fed through one of two filters before being buffered
and sent to the Main Output Circuitry. The two filters are:
•A 9
th
order elliptical filter with a cutoff frequency of 23.5 MHz. This
filter includes sin (x)/x correction. This filter is used for continuous
sine and squarewaves.
•A 7
th
order linear phase filter with a cutoff frequency of 12.5 MHz.
This filter is used for ramp, noise, and arbitrary waveforms.
A portion of the output sine wave is squared by a comparator and used to
create a variable duty cycle signal used by the Synthesis IC to create the
squarewave, pulse generator clock, and sync signals.
The squarewave DAC output is split into two opposite value signals and
applied to a multiplexer. The output of this multiplexer is a square wave
or pulse signal with the correct duty cycle. The rising edge and falling
edge of the signal are adjusted and the signal is buffered and sent to the
Main Output Circuit.
The Main Output circuit accepts one of two inputs; the sine/arb
waveform or the squarewave/pulse waveform. Once selected, the signal
can be applied to one or both attenuators and/or a +20 dB amplifier. The
attenuators and amplifier are used to create the requested output signal
amplitude.
The output is protected by a relay. When the relay is open, the
instrument can read the value of the Main Output Circuit. The output
relay is opened on user command, if a current overload is detected, or if a
voltage over–range condition is found.
Offset <2.5 V Offset >2.5 V
Amplitude Range
(Vpp into 50 Ω)
–10 dB –20 dB Amp –10 dB –20dB Amp
10 V to 3.16 V Out Out In Out Out In
3.16 V to 1 V In Out In In Out In
1 V to 0.316 V Out Out Out Out In In
0.316 V to 0.1 V In Out Out In In In
0.1 V to 0.0316 V Out In Out
0.0316 to 0.01 V In In Out
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