Chapter 8 167
Hardware Options
Verifying Option 107 Audio Input
Verifying Option 107 Audio Input
The PSA must have Option 233, Measuring Receiver Personality
installed in order to enable Option 107, the Audio Input. Option 233
will always be present since the Audio Input Option 107 is only
available on instruments that have Option 233. Option 233 is the
built-in measuring receiver personality that is required for a PSA that
is part of the N5531S Measuring Receiver System. Unlike many
measurements where you can see a trace or waveform, the results of the
audio measurement are displayed as numbers on screen.
Measurements include: Audio Distortion, Audio Frequency, Audio AC
Level, and Audio SINAD.
Option 107 consists of an Audio board and a front panel BNC connector.
The Audio signal path is in addition to, and completely bypasses the
normal RF/IF signal chain. The frequency range is 20 Hz to 250 kHz.
Usable amplitude range is 0.1 V rms to 3 V rms. The input impedance
of the audio input is 100 k ohms. The effect of this 100 k ohm input
impedance is important to take into consideration when making
measurements since most test equipment such as a function generator
has 50 ohm input impedance. Therefore, if a function generator with 50
ohm input impedance is set to a particular output level and connected
to the Audio Input port of the PSA, the PSA Audio AC Level
measurement will yield a reading that is two times the function
generator setting.
The Audio signal comes from the front panel BNC connector, goes to the
Audio board where the signal is buffered, level shifted (5 gain levels
provide best signal to ADC), then run through an ADC followed by an
FPGA (a custom gate array) that provides filtering and decimation to
the ADC bits. The time domain FPGA bits are sent to the PSA CPU
assembly via the PCI bus and the results of the measurement are
displayed on screen.
Figure 8-1 Option 107
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