An advanced monolithic fm IC for high quality broadcast receivers

Microelectronocs and Reliability,

Vol. 16, pp. 345-366. Pergamon Press, 1977. Printed in Great Britain,

AN ADVANCED MONOLITHIC FM IC FOR HIGH QUALITY BROADCAST RECEIVERS L.R. A v e r y RCA Limited, Sunbury-on-Thames, Middlesex TW 16 7HW, England

Introduction

This paper describes a state of the art

fm if linear integrated

circuit intended for use in the next generation of the highest quality broadcast r e c e i v e r s .

The device, type CA3189E, has been developed following

discussions with manufacturer of high quality audio equipment currently using the CA3089E.

Attention has been paid to optimising the performance

of each section of the device whilst maintaining flexibility to satisfy different manufacturers' requirements.

Where appropriate details of the design

c r i t e r i a and optimisation are given.

Features

The CA3189E quadrature meter

detector,

output,

features

a high gain limiting if amplifier,

aft output,

adjustable

threshold

separate delayed

audio output, rf agc,

single coil

signal level "S"

noise mute

and deviation

mute.

If Limiting Amplifier

The if amplifier consists of three differential amplifier stages providing typical input limiting sensitivity of 12pV. The input stage, shown in Fig. i is a cascode circuit to provide low input capacitance-for use with ceramic filters - with high gain.

Q1 and Q2' the input transistors, are

optimised for low emitter-base input capacity consistant with high frequency performance and low noise.

The emitter-base input capacity is mainly

determined by the emitter area and hence should be as srnall as possible. However, for minimum noise rbbt should be very low which requires a multiple base contact, many emitter striped device resulting in a high input capacity.

The optimum for the present application is a single

emitter stripe 3 - 5 squares long with two base contacts symmetrically 345

346

L.R. Avery

placed each side of the emitter. Relatively high vaiues of load resistance (2K) are used so that the required gain m a y be achieved in three stages.

Darlington emitter

followers are used to provide buffering and dc level shifting to the following stage as s h o w n in Fig. 2. O n e p r o b l e m with any wide band high gain limiting amplifier with no interstage filtering is noise.

If the amplifier bandwidth is m a d e sign-

ificantly higher than the operating

if frequency two otherwise out-of-

band signals can be mutliplied together resulting in a noise c o m p o n e n t which is no w in the pass band.

This is s h o w n diagramatically in Fig. 3.

Obviously the higher the amplifier gain the w o r s e this p r o b l e m b e c o m e s as considerable care is necessary to limit the if bandwidth whilst maintaining phase linearity (constant group delay within the pass band).

The

typical limiting sensitivity chosen, 12~V, with an if bandwidth curtailed above 1 5 M H z romise.

has been found to provide the o p t i m u m p e r f o r m a n c e c o m p -

Restricting the if bandwidth has the added advantage that the pc

board layout requirements are not critical as the C A 3 0 8 9 E

with its 2 5 M H z

bandwidth.

D e v i a t i o n and N o i s e Muting

The limited

carrier

a suitable been

noise

muting

or sufficient

muting

adjusted

the mute

signal.

voltage

excellent

muting

tuning

when

it can be seen

voltage

to a demuting

receive

the correct

sufficient

tuning

shows tuned

circuit

equivalent taken

in the audio

the loudspeaker demuting through

unless

action. a station;

Examining

prior

output

was

output steps

point. which

are

120mV circuit

but is not so good Refering

the audio

mute

the mute

is tuned

output

more

output

than 300KHz at pin 6 under

is considerably

to the demuting being

removed

dc shift has an annoying

to reduce occurs,

the dc level at the audio

action

the speed

but in reverse

output

slowly

from the

of the

held at the reference

can cause

for

to Fig. 5,

signal the noise

A sudden

taken

the same

has

dc level is in fact following

But,

tuning

Obviously

The

circuit

This

signal.

that the dc level

the audio

to the correct

place

astrong

mute

about

muting

the receiver

point.

"S" characteristic.

mute

noise

to provide

in Fig. 4.

signal level to return

point,

carrier

of a

falls below

as shown

of a strong

level whilst

an absence

of the noise

signal level

for interstation

condition

noise

the rms

on pin 12 rises

that of the correctly detector

sensitivity

that in the presence

may

detecting

in a fully limited

into or out from

circuit

this tuning

relies upon

holes

The

so that when

output

is therefore

from

circuit

level

therefore "thump"

in

of the muting/ when

changes

tuning during

Advanced Monolithic f/m IC for High Quality Receivers

tuning until the edge of the "S" curve appear

in the carrier

again returned One

circuit between

time constant preferably mute

in Fig. 6.

may

circuit so that a worst

be unacceptable

could be used

However,

case 2v dc shift can

requires

when

manually

if the dc shift were

less than the peak audio output.

to sufficiently

a relatively long time fast tuning.

considerably

A smaller

smaller

This is achieved

and

by the deviation

circuit. The

reference

deviation mute

sources

Q96

and Q93

equal upper

level.

withQ101

forms

The

upper

reference

from

provide

reference

comparator.

comparator.

The

A 15K

by varying

resistor

of

establishes

about the pin i0 afc

voltage is fed to the base Of Ql00 Similarly

common

pin 7 and the outputs are ORED

can be controlled

in Fig. 7. Current

R76 and R77

levels symmetrically

With this arrangement

tuning afc reference,

and sink an identical current

flowing through

reference

the upper

the lower

into pin 12.

reference

determined

the afc circuit as shown

This current,

and lower

reference

is taken

respectively

700uA.

of two accurately

placed about the correct

and an input from

approximately

pin I0.

circuit consists

levels symmetrically

two comparators

form

control voltage by placing an

without any noticeable "thump"

constant which

above

logic output at pin 12 and the audio

control input at pin 5 as shown

be handled

due to the action described

of the mute

the mute

slow the action of the muting

sufficient holes

level.

the "thump"

the rate of change

integrating mute

of reducing

When

output goes high and the audio output is

to the reference

way

is to reduce

the mute

is reached.

347

Q97

which,

andQ98

input for the comparators

via current

mirror

Q102'

QI03

the sensitivity of the deviation mute

the value of resistance

gives a typical deviation

placed between

circuit

pin 7 and

sensitivity of +40KHz

as shown

in Fig. 8.

Audio

Amplifier

Circuit

During

discussions

ent (and predictable) the cause

with receiver

manufacturers

there was

plea for better noise performance.

of excessive

noise in the CA3089E

a consist-

Investigations

revealed

three main

into

sources;

the if (which has been dealt with above) the internal stabilised regulator the audio amplifier The main zener changed

diode.

The

itself.

cause

of the noise in the regulator

construction

to reflect our current

Additionally

of the zener knowledge

the audio load resistor

pin 6 and pin I0 thus providing pin I0 and thereby

and

improving

is now

circuit is clearly the

in the CA3189E

has been

of low noise zener

design.

connected

the opportunity

externally

of decoupling

the signal to noise ratio.

between

any noise at

Experience

with

L . R . Avery

348

d e v i c e s f a b r i c a t e d to date h o w e v e r i n d i c a t e s that only a half to one dB i m p r o v e m e n t can be m a d e in the S/N r a t i o by d e c o u p l i n g pin 10. The audio a m p l i f i e r and m u t e c i r c u i t a r e shown in Fi~. 9.

(~46

and Q53 p r o v i d e the a n t i p h a s e audio s i g n a l s which a r e fed to ~ 4 8 ' (-~48A and Q49' Q49A which form the dc v o l u m e c o n t r o l for the audio mute circuit.

The output from (~48 is a c c u r a t e l y m i r r o r e d to p r o v i d e a push

pull output c u r r e n t from Q49 and (~83 al pin 6.

This a r r a n g e m e n t gives

the added f l e x i b i l i t y that the r e q u i r e d audio output can be o b t a i n e d by v a r y i n g the load r e s i s t o r .

If c a r r i e r f i l t e r i n g is a l s o i m p r o v e d by the

u s e of low ft pnp l a t e r a l t r a n s i s t o r s (~48 and Q49 in the audio s i g n a l path. Audio m u t i n g is a c h i e v e d by Q80"(~81

When (°)'81 t u r n s on and the

v o l t a g e drop a c r o s s R64 e x c e e d s thai a c r o s s R63 Q48A and 6~49A t u r n on and d i v e r t the audio s i g n a l c u r r e n t from Q46 and Q53 to ground.

When

Q48 and Q49 a r e c o m p l e t e l y off no audio s i g n a l is a v a i l a b l e at pin 6 and pin 6 dc voltage is equal to the r e f e r e n c e voltage at the o t h e r end of the audio load r e s i s t o r .

Tuning

Meter

The from

(Signal Strength)

tuning

the output

meter

Under summer

ideal zero

signal

the rf and

available

under

zero

zero

signal

conditions

application

mixer

built into the meter

stages,

200)~A and

in a practical

icularly

limiter

of three

amplitude

a current

detectors

summer

fed

and an output

in Fig. I0.

is approximately

However,

under

circuit consists

of the three

level shifter as shown

Circuit

stages,

signal

the voltage noise

results

conditions

d.rive circuit conditions.

the current

from

across earlier

therefore

adc

is 0.4volts

stages,

part-

current

being

Offset has to be

is to show

typical meter

the current

R61

in a far higher

if the meter

The

from

a true zero

characteristic

of the

CA3189E only is shown in Fill, 11.

R.F.

AGC C i r c u i t

During disagreement

discussions

this was

control

started

voltage

and

manufacturers

fixed at approximately at 4.5v.

in Fig. 12 - provides

threshold

receiver

on only one point - the threshold

In the CA3089E

shown

with

provides

user

The

a dc output

suitable

was

level of the rf agc 10mV

circuit employed

flexibility

there

circuit.

if input and

the rf

in the CA3189E

in controlling for obtaining

major

the rf

-

agc

at least 40dB

of

Advanced Monolithic f/m IC for High Quality Receivers

c o n t r o l w h e n u s i n g G 2 of a d u a l g a t e m o s f e t The point at which rf agc occurs

rf stage.

can be chosen by the designer

f e e d i n g a s u i t a b l e c o n t r o l v o l t a g e i n t o p i n 16. required

a t p i n 16 i s 1. 3v in t h e s e n s e t h a t

The threshold

by

voltage

voltage rising from below

t h i s v a l u e to a b o v e it w i l l c a u s e t h e o n s e t a n d c o m p l e t i o n

of r f a g c a t p i n 15.

T h e i n p u t c o n t r o l v o l t a g e m a y b e o b t a i n e d f r o m p i n 13, in w h i c h case the threshold 200mV

if i n p u t ,

l e v e l c a n b e v a r i e d f r o m a n o m i n a l 200)~V or from an external

Typical Application

if i n p u t to

source.

Circuit

A typical application c i r c u i t is shown in Fig. 13.

Potentiometer

P2 sets the r f agc threshold and P2 the noise mute threshold.

Resistor

R 3 between pin ? and pin i0 sets the deviation mute threshold and R4 is used to set the r e q u i r e d level of r e c o v e r e d audio. F o r c o r r e c t c i r c u i t operation it is n e c e s s a r y to fully decouple the audio output normally p r e s e n t at pin 7 otherwise audio muting will occur on peak deviations. Additionally some means should be provided for adjusting any small dc offset which may be p r e s e n t between pin 6 and pin 7 and would e i t h e r affect the audio dc output level or the deviation mute symmetry.

A recommended layout is shown in Fig. 14.

Typical S/N ratio and am r e j e c t i o n c u r v e s a r e shown in Fig. 15 and r f agc c h a r a c t e r i s t c , open loop, with the threshold set by P2 to lmV is shown in Fig. 16. With the single coil detector c i r c u i t shown in Fig. 13 the typical t h i r d harmonic distortion is 0.3%.

This can be reduced to l e s s than 0. 1%

by using the bandpass coupled detector c i r c u i t as recommended for the CA3089E.

Conclusions

The CA3189E r e p r e s e n t s the state of the a r t in high quality fm if c i r c u i t s and has been designed, a f t e r full d i s c u s s i o n s with the r e c e i v e r m a n u f a c t u r e r s , to provide the highest possible p e r f o r m a n c e at minimum cost.

349

350

L . R . Avery

References

R C A C A 3 0 8 9 E D a t a s h e e t F i l e No. RCA C A 3 0 8 9 E A p p l i c a t i o n s

Note ICAN

Acknowledgements

The

author

in specifying devices and

to thank

the requirements

during

L. Baar

wishes

engineers

of the CA3189E

the development

for their valuable

those

phase. assistance

He

in industry

who

and

in evaluating

also wishes

to thank G.Granger

in processing

<

R6

R7

<

2K

2K

BIAS

and testing,

TO 2ND STAGE

BIAS

R

R2 28K R1 28K FIG. 1

helped

CASCODE INPUT STAGE

FEEDBACK FROM LAST IF STAGE

Advanced Monolithic f/m IC for High Quality Receivers

< RIO < 2K

35]

Rll 2K

FROM 1ST STAGE TO 3RD STAGE

Q8

I

2K1

I

I

I

Q10

< 2K1

,

< R13 : 2K1

Q7

.

~> R14 < 533

]

<~R12 > 2K1

FIG. 2 ILLUSTRATING DARLINGTON EMITTER FOLLOWER BUFFERS

352

L . R . Avery

e I A N D e 2 A R E TWO NOISE COMPONENTS N O R M A L L Y O U T OF B A N D WHICH C A N PRODUCE e3 (e3 - e 1) DUE TO NON L I N E A R A C T I O N OF THE L I M I T I N G A M P L I F I E R . A M P L I T U D E S NOT TO SCALE.

==

--~

~

IF B A N D W I D T H e2

J

eI

e3

= f

FIG. 3

I L L U S T R A T I N G THE G E N E R A T I O N OF A D D I T I O N A L NOISE COMPONENTS

PIN 12 VOLTS

5.6V 5-

4

32-

10

I

80 mV FIG. 4

150 mV

NOISE MUTE OUTPUT VOLTAGE (PIN 12) VERSAS PIN 9 IF VOLTAGE

PIN 9 VOLTS (mV rms)

Advanced Monolithic f/m IC for High Quality Receivers

;~,~,OT~..%G

~

NO,SEMUTEOPERATESCLOSETOPEAKS

AUDIO DC HELDAT THIS ~ LEVEL RETWEEN STATIONS ~

DETECTOR'S'CURVE(STRONGSIGNAL) \

~/

\ I

Iv.~/-

NOISEMUTEOPERATES

AUDIO DC

AUDIODC LOWPRIORTO MUTING

FIG. 5 OPERATINGPOINTSOF THE NOISEMUTECIRCUITON DETECTORSCURVE

470 PIN 12

i

INTEGRATING RC NETWORK TO SLOW ACTION OF MUTE CIRCUIT

~

l

• PIN 5

A, FIG. 6 INTEGRATINGNETWORK USEDTO SLOWACTION OF MUTE CIRCUIT

353

354

L.R.

Avery

~~Q103

R75

ao~ Qloo R76 1K

TO PIN 10 o97

FROM NOISE MUTE CIRCUIT

Q98

TO PIN 7

Q104

R73

~ R78

R79

FIG. 7 DEVIATION MUTE CIRCUIT

PIN12

FIG. 8

_~oo~.z_,o~.z, o~o~~.z

CURVE

A U D I O DC REFERENCE LEVEL

\

ILLUSTRATING REDUCTION OF DC SHIFT IN A U D I O OUTPUT A C H I E V E D BY D E V I A T I O N MUTE

AUDIO DC SWITCHING LEVEL REDUCED FROM A TO B BY D E V I A T I O N MUTE CIRCUIT

A

u~

(0 t--.° <:

('b

,O (:::

0~"

El

;::r'

O p-=

O...

356

L.R.

Avery

< < R44 46 ~__.,Q,53

~ R63

V+ I FROM PIN 5

R64

R65

)'79

0'8~Q81

TO PIN 6 Q83

< < R66 >'R67 R4o

FIG. 9 AUDIOAMPLIFIERCIRCUITDIAGRAM

Advanced Monolithic f/m IC for High Quality Receivers

R60

B9

FROM lSTSTAGE LEVEL DETECTOR

357

S J K

FROM 2ND STAGE LEVEL DETECTOR <

R61A

FROM 3RDSTAGE LEVEL DETECTOR

< R61 TO PIN 13

i FIG. 10

METER DRIVE CIRCUIT

R62

1( JV

0

1.0

2.0

3.0

4.0

5.0

FIG, 11

100~uV

10mV

TYPICAL SIGNAL STRENGTH METER C H A R A C T E R I S T I C - PIN 13

I mV

100mV

Advanced Monolithic f/m IC for High Quality Receivers

359

V+

•

R82

ol

FROM TEMP COMP VOLTAGE REF

>

°8 RF AGC • CONTROL OUTPUT PIN 15 RF AGC O ' CONTROL INPUT PIN 1 6

~ Rso

R85 LQ106

Q105,.,~

R84

FIG. 12 RF AGC CONTROL CIRCUIT

IF :ILTER

'ROM

,,~2 0n

33K

RF AGC -,,~---j

T

.--L-- 10n

TO SUIT FILTER

,

.~A3189E

220K

TOKO 144 LZ

I'0 SUIT METER

10n

47

--


)

4,

3K9

-tH

3;

==[=1/J

.~2K

IOnF

R4

-

I

P1 10K

= AUDIO

'~ AFT

TYPICAL APPLICATION CIRCUIT

--~-- CDemphasis

•

.~

68K

10n & ! 0 . u

FIG. 13

&

KACS K586 HM

~TOKO

4-12V

36]

Advanced Monolithic f/m IC for High Quality Receivers

IF LIMITING AMPLIFIER FEATURES •

HIGH GAIN LIMITING IF 12~V typ.

• • • • • • •

SINGLE COIL QUADRATURE DETECTOR AFC OUTPUT SEPARATE AUDIO OUTPUT (PROGRAMMABLE LEVEL) SIGNAL STRENGTH 'S" METER OUTPUT ADJUSTABLE THRESHOLD DELAYED RF AGC INTERSTATION NOISE MUTE PROGRAMMABLE DEVIATION MUTE

.\.\ \

RELATIVE BANDWIDTHS OF CA3089 AND CA3189

CA3O.,

362

L.R.

Avery

O-

/! /

-10-

F.M. + 75 KH

/ CA3189 O N L Y CA3189 PRECEDED BY FILTER A N D GA I N STAGE

-20 -

\ -30 -

lb. k0

-40-

> t-<

\ \

\ \

\

--I W

n,-

J~z

z~

NOISE

J j

-50

\

\

\

-60

\ \

\ \

-70 -

\ -80 l/iV

I

I

I

I

10pV

100pV

1mY

10mY

S I GN A L LEVEL FIG. 15a

SI GN A L TO NOISE R A TI O

I

100mY

CD

-I U,I

>

141

O

I.-,

I-

lpV

-60 -

-40-

-20-

0-

FIG. 15b

10

g

100

I

T Y P I C A L A.M. R E J E C T I O N C A 3 1 8 9

Y

SIGNAL INPUT

/

lmV

I

A.M. 30% M O D

F.M. -+ 7 5 KHz

\

J

10

]

100 L~

r~

=::t O

O.,

g.

E..

z

t--

1CL~V

1

2-

3-

4~

5

6-

7-

8-

FIG. 16

100.uV

TYPICAL OPEN LOOP RF AGC CHARACTERISTIC

1mY

i

10mV

r

100mV

.-<:

4L~

~OCKET

P

N+

EP!

NPUT TRANSISTORS

:~)CKET

P

P+

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r~

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<~

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--80

--40-

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40-

80-

120-

160-

i

--60

I

-80

I

--100

I

--40

I

I

10.7 MHz

L

+20

C H A N G E IN FREQUENCY ,~ f (KHz)

-20

L

+40

I

+60

I

+80

I

+100

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