Agilent Technologies 856290216 service manual Adc Asm, 26 ADC/lnterface Section

ADC ASM

Refer to function block F of A3 Interface Assembly Schematic Diagram in the

HP 8560 E-Series Spectrum Analyzer Component Level Information.

1. Press (PRESET) on the spectrum analyzer and set the controls as follows:

Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60s Detector mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAMPLE

2.Check that HSTART-SRC (U504 pin 4) goes TTL high, causing HHOLD (U506 pin 16) to go high 15 ps later.

3.Check that HSTART-ADC (U506 pin 15) goes TTL high 19 ps after HSTART-SRC goes high.

4.HHOLD should stay TTL high for approximately 18 ps, and HSTART-ADC should stay high for approximately 31 ps.

5.Check that LCMPLT (U504 pin 15) goes TTL low 12 /JS after HSTART-ADC goes high (12 bits at 1 ps per bit). LCMPLT indicates that the successive approximation state machine (SASM) has completed the ADC conversion.

6.Check that LDONE (U506 pin 19) goes TTL low approximately 2 ps after LCMPLT goes low.

ADC

Refer to function block A of A3 Interface Assembly Schematic Diagram in the

HP 8560 E-Series Spectrum Analyzer Component Level Information.

The successive approximation state machine (SASM) consists of A3U527 and A3U528. Upon the occurrence of HSTART-ADC, the SASM successively toggles bits from high to low starting with the most significant bit. The digital result is then converted to an analog current in DAC U518 and compared with the SAMPLED VIDEO. If the DAC current is too high, the output of U512 will be low, telling the SASM that the “guess” was high and that the bit just toggled should remain low. It then moves on to the next most significant bit until all 12 bits have been “guessed” at. Each “guess” takes 1 ps (one cycle of HBADC-CLKO), or 12 ps to complete a conversion. When the conversion is completed, the SASM sets LCMPLT low. The bits are written to the data bus by buffers U514 and U516.

1. Set the spectrum analyzer controls as follows:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MH z

Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 s Detector mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAMPLE

2.Trigger an oscilloscope on HSTART-ADC (U506 pin 15) and monitor the outputs of the SASM (U527 pins 18 and 19; U528 pins 14 through 23). Each bit should start high and be switched low. It will either stay low or return to a high state 1 ps later, depending on the comparison at U512.

3.If the outputs do not exhibit this bit pattern, and the ADC ASM checks are working properly, suspect A3U527, U528, or one of the latches (U514/516). If the output of

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