Racal Instruments 9916 - CHAPTER 3 The CDI Chip

Racal Instruments 9916

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THE

CDI CHIP

3.1

A

basic

digital

frequency

meter

comprises a

chain

of

de<;:ade

counters

feeding

b.c.d.

data

into

latched

stores.

Counting

is

controlled

via

a

main

gate

which

is

opened

for

a

period

determined

by

the

time

base.

Provision

is

made

for

resetting

the

counter

and

releasing

the

data

for

display.

In

the

9916

these

functions

are

carried

out

in

the

integra'ted

circuit

lC4,

which

achieves

large

scale

integration,

using

the

col

lector-

diffusion-isolation

principle.

For

convenience,

IC4 will

often

be

referred

to

in

the

handbook

as

the

'CDI

Chip'.

Fig

3.1

is

a

simplified

diagram

of

the

frequency

measurement

mode,

showing

the

principal

functions

performed

by

the

CDI

Chip.

c:;=

'SPLAY

MULTIPlEXED

BeD

OUTPUT

DATA

I

STORES

I

I

I~PUT

INPUT

(JATE

1

CIRCUITS

COUNf(R

I

CONTROL

I

I I

FREOUENCY

I

I

CD I

TlHE

8ASE

'So

TANOARQ

I

CHIP

Ext£RNAl

t;

1

STANDARQ

,

Y

,.

).

LINE TIME

BASE

SELECTiON

·9916

Vol.

2

Basic

FrequencY

~eter

Fig.

3.1

3-1

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