Keithley 2015, Service Manual

Page: 79 / 158

4-16 Troubleshooting
Sine generator circuitry
Refer to Figure 4-6 for the following discussion on the sine generator circuitry.
Figure 4-6
Sine generator circuitry block diagram
Sine generator
Y302 is a fixed frequency clock that forms the input to U301, the adjustable frequency sine
wave generator. The sine wave generator' s frequency is set by the microprocessor through the
FPGA, U334, and the opto-isolators U304, U320, and U321.
Attenuator
U303, U334, U335, and U302 form the adjustable attenuator that adjusts the sine wave output
amplitude. The output amplitude is set by the microprocessor through the FPGA, U334, and the
opto-isolators U304, U320, and U321.
Inv Sine/
Pulse
Out
Inv-Sine/pulse
Comparator
K301
50/600 Ohm
Source
Output
U305
U306
U307
U308
Filter
U307
Attenuator
U303, U334
U335
Sine Generator
U301
OSC
FPGA
Distortion Digital Circuitry
(see Figure 4-4)
EEPROM
+1
-1