Table of Contents
Advertisement
The trigger circuitry output drives the time base and the logic analyzer arming
input. This output and internal status signals are interfaced to the data bus for
software processing purposes.
Time Base
The time base provides the sample clocks and timing necessary for data
acquisition.
It consists of the 400 MHz reference oscillator, mux/sync hybrid
(multiplexer/synchronizer),
and time base IC.
The mw/sync hybrid provides sample clocks to the ADC. At sample rates of 400
MHz and 200 MHz, this sample clock is derived from the 400 MHz reference
oscillator.
At 100 MHz and slower, the sample clock comes from the time base IC.
The mux/sync hybrid synchronizes the gating of the sample clock to provide only
full sample clocks.
The time base hybrid has programmable
dividers to provide the rest of the sample
frequencies appropriate for the time range selected. It uses the time-stretched
output of the fine interpolator
to time-reference
the sampling to the trigger point.
It has counters to control how much data is taken before (pre-trigger data) and
.
after (post-trigger data) the trigger event. After the desired number of pre-trigger
samples has occurred, the time base hybrid sends a signal to the Logic Trigger
(trigger arm) indicating it is ready for the trigger event. When the trigger
condition is satisfied, the Logic Trigger sends a signal back to the time base hybrid.
The time base hybrid then starts the post-trigger delay counter. When the
countdown reaches zero, the sample clocks are stopped and the CPU is signaled
that the acquisition is complete.
Fine
Interpolator
The Fine Interpolator
is a dual-slope integrator that acts as a time-interval
stretcher. When the trigger circuitry receives a signal that meets the programmed
triggering requirements,
it signals the time base. The time base then sends a pulse
to the fine interpolator.
The pulse is equal in width to the time between the trigger
and the next sample clock. The fine interpolator
stretches this time by a factor of
approximately
375. Meanwhile, the time base hybrid runs a counter with a clock
derived from the sample rate oscillator.
When the interpolator
indicates the
stretch is complete, the counter is stopped. The count represents, with much
higher accuracy, the time between the trigger and the first sample clock. The
count is stored and used to place the recently acquired data in relationship
with
previous data.
Probe
An oscillator generates a 1.25 kHz square wave with fast edges for oscilloscope
Compensation
probe compensation.
The oscillator's levels range from approximately
-400 mV to
-900
mV.
Digital
Interface
The Digital Interface provides control and interface between the system control
and digital functions in the acquisition circuitry.
Analog
Interface
The Analog Interface provides control of analog functions in the acquisition
circuitry.
It is primarily a 16 channel DAC with an accurate reference, and filters
on the outputs. It controls channel offsets and trigger levels.
Theory of Operation
6A-10
HP
16526/16538
Service Manual
Advertisement
Chapters
Table of Contents
