HP 3562A Service Manual page 267

C I RC U I T D E SCRI PT I O N S
Baseband
Zoom
I nput Signal
From ADC Board
Signals From
LO Board
(Freq.=Center Freq.J
Figure 6-ASb Zoom Implementation
W hen he processed data is ready for storage, the control l e r IC s req uest the d i gital fi lter
l ocal data bus. When granted use of the bus, the contro l l e r I Cs transfer the data to the
g lo bal data bus i nterface. The global bus DMA control l e r sends a m emo ry req uest to
G l o bal RAM . When G l obal RAM retu rns a mem o ry grant, the data f l ows on the g l obal
d ata bus to G lobal RAM.
f i l ter data busses . The rem a i nder of the process is the same as described prev i o u s ly.
AS,
Digital Filter Block Descriptions
Refer to fig u re 6-ASc, AS B l ock Di ag ram , for the following ci rcuit bloc k descriptions.
D I G ITA L F I LT E R
E a ch d igital fi lter cons ists of a contro l I C and two fi lter I Cs, one for real data and one
for im agi nary data. When i n the zoom mode, the f i l ters mu lti ply the i n put data by a d igita l
s ine (real) and cos ine (im a g i n ary) f u n ction from the LO assem b ly.
6-46
If fi ltering is req u i red and the frequency span is 1 00 kH z, the f i l ter
control ler passes the incom i ng d ata to the fi lter ICs in serial form at.
The fi lter I Cs m u l tiply the incom i ng data by the LO data s i g n a l . T h i s
sig nal is a constant when not i n zoom . T h e fi lter I Cs fi lter the data
and retu rn it to the control ler IC Depend ing on the processing req u i red,
this may be a m u ltipass operation. The control ler IC converts the
fi ltered data to a paral l e l form at.
Zoom is u sed when the selected span is less than 1 00 k H z . The fi lter
controller passes the data to the fi lter I C s in a serial format. The fi lters
down- convert the i n put data by m ixing it with a d i gital representation
of the span cente r freq uency from the LO board. The resu ltant sum
and d iffere nce are fi ltered to remove the sum com ponent and yield
a red u ced freq uency span. See figu re 6-ASb. The fi lters retu rn the
processed data to the control l e r I C, w h i c h converts the data to a
para l l e l format.
{
Sin
Real
Filter
I mag
Filter
. . j· a . . . ·tl+E
MO D E L 3S62A
Data Ready For
Single Channel
Complex FFT; Yields
Frequency Span Other
Than 0-1 00 KHz