HP 3562A, Service Manual

Page: 263 / 570

MODE L 3562A C I RC U I T D E SC R I PT I O N S
Phase Accumulator
The phase accumulator uses six internal registers with adders and latches to produce phase
val ues (addresses). One or two registers (depending on mode) contain the phase values
which are used to generate the desired sine and cosine values. The other registers contain
phase increments, i ncrements of phase increments (ch i rp mode), or are not being used.
These phase i ncrements deterrl1 ine the sine wave frequency (frequency
=
AS/AT, where
AT is the sample period). The only m ode in which all registers are used is the chirp mode.
The registers are 64 bits, but only the chirp sweep rate uses 64 bits. A l l other val ues use
the 32 MS B. The data is hand led in fou r, 8-bit chu nks each cycle.
Sine ROM (U29, U20J
The sine ROM (U29, U20) takes the phase val ue from the phase accumulator a nd uses
it to output a digital sin usoidal wave. The sine ROM contains the positive half of a sine
wave in a lookup tab le. The sine ROM takes in 1 3 phase bits (an add ress) and outputs
1 6 ampl itude bits (data).
Interpolator and Adder
The interpolator is used to increase the phase resol ution of the sine ROM output and
produce the data needed for a com p l ete sine wave. The interpolator ROM(U1 3) uses the
output from the phase accum u l ator to prod uce an interpol ate val ue. This value is added
to or subtracted from the sine ROM o utput to prod uce the high resolution output (parallel,
1 6-bit word) i n four, 4-b it chu nks.
Output Buffers
The output buffers consist primarily of three, 1 6-b it para l lel-in, serial-out sh ift registers
and an output tim i ng PA L (A4 US8). The tim ing PAL contro ls the sh ift registers and the
self-test shift registers.
Control Circuits
The control circu its consist of two PALs, one PLA, and some related circuitry. The function
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Phase Acc u m u l ator PAL (U56)
I nterpol ator PAL (U55)
T i m i ng PAL (U68)
This PAL controls the input, output, and s h ifting
of the data i n the phase accum u l ator.
This PLA controls the addition, subtraction, and
slope functions for the interpolator output and
other random logic functions.
This PAL produ ces the basic timing signals of
the LO.
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