Agilent N5161A/62A/81A/82A/83A MXG Signal Generators Service Guide
Troubleshooting
Overall Block Description
1-5
The reference output signals are multiplied to provide the following signals:
•
50 MHz reference signal to the synthesizer Frac-N and FM circuitry
•
1 GHz LO signal to the heterodyne (HET) band mixer
Synthesizer Circuitry
The frequency synthesis circuitry is based on a phase-locked loop (PLL). It uses a Frac-N synthesis FPGA to control the multiplier and
divider module. Frequency multipliers and dividers are used to extend the basic synthesis loop frequency range to cover 250 MHz to 6 GHz.
Frequency and phase modulation are built into the synthesizer circuitry using the Frac-N FPGA.
•
The VCO tunes over a range of 750 MHz to 1.5 GHz.
— From 250 MHz to 375 MHz, the VCO is divided by 4.
— From 375 MHz to 750 MHz, the VCO is divided by 2.
•
The PLL operates over a range of 1.5 GHz to 3 GHz.
•
The heterodyne band provides frequencies from 100 kHz to 250 MHz and operates over a VCO range of 1.0001-1.25 GHz. The 100 kHz
to 250 MHz signal is obtained by mixing the heterodyne band with the 1 GHz LO signal provided by the reference circuitry. The
resultant IF signal is then amplified to provide the 100 kHz to 250 MHz RF signals.
Output Power Leveling Circuitry (Automatic Leveling Control Circuitry) < 3.2 GHz
The A3 RF assembly contains the ALC modulator diode for frequencies < 3.2 GHz. ALC operation is similar to that in the
N5161A/62A/81A/82A except that the ALC control circuitry and coupler detector are located on the A7 Micro Deck.
The circuitry that creates pulse waveforms is located on the A3 RF assembly as is the pulse modulator for frequencies < 3.2 GHz. The pulse
modulator for frequencies > 3.2 GHz is located on the A7 Micro Deck.
Pulse Modulation
Pulse modulation drive for all frequencies is developed on the A3 RF assembly. For frequencies
≤
3.2 GHz, the pulse modulator diode is
located on the A3 RF assembly.
Amplitude Modulation
The AM drive signal is generated on the A3 RF assembly, routed to the ALC assembly on the A7 Micro Deck, and then applied to the ALC
modulation diode on the A3 RF assembly.
Frequency Modulation, Phase Modulation, Phase Noise, and Switching Speed
The A3 RF assembly determines the signal generator’s FM,
Φ
M, Phase Noise (single sideband and residual phase noise), and switching
speed performance.
A4 Internal Memory Card (N5162A/82A Only)
1
The A4 Internal Memory Card supplies additional non-volatile memory. It is a USB 2.0 compliant flash card with 800 MSa; equivalent to
4 GB.
1
For instruments with serial prefixes <US/MY/SG4818, the persistent memory value is 512 MB (102 MSamples).
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