VTSH7UZ50 - Sharp Electronics Corp.

VTSH Series

RF A ppl ica tion Note Internal-PLL Electronic Tuners

Tune rs Using the Motorola ® MC4 4817D Phase-Locked Loop

SHARP Electronics Corporation, Microelectronics Group, RF Products Marketing Group, 360-834-2500

OVERVIEW

This Application Note covers VTSH-series tuners

which utilize the Motorola® MC44817D Phase-Locked-

L oop (P LL) In tegrated C ircu its (ICs). Al l of th e Sharp

products covered here are useful for Te le v is ion, V id eo

Cassette Recorders, Multimedia, or other similar

a ppl i cations tha t req ui re a fi rst-conversion stage.

INTRODUCTION

SHARP’s VTSH series of tuners use the same

Motorola PLL IC for a variety of tuner application

types. These tuners operate in similar manner, with

variations dependent on the destination country. All the

PLL devices are programmed in a similar manner , with

the frequency step dependent on the application.

VTSH Series

Ta ble 1. PLL Spe cifications

TUNER PA RT

NUMBER TYPE CRYSTAL

REFERENCE

FREQUENCY STEP SI ZE

VT SH 6U Z6 0 NT S C 4 MHz 62.5 kHz

VT SH 7U Z5 0 NT S C 4 MHz 62.5 kHz

VTSH6HZF1 PA L 5.5 3.2 MH z 50 kHz

VT SH 7U F5 6 NT S C 4 MHz 62.5 kHz

The VTSH series of tuners are PLL-tuned and cover

the VHF and UHF frequency bands. A total of 181

standard North American NTSC-M channels are within

the 55.25 MHz to 801.25 MHz tune range of the

VTSH6 U Z60, V TS H7 UZ 50, and V TS H7UF56 mode ls.

The VTSH7UF56 has an F-connector in put inst ead of

the s ta ndard RC A con nector. Ch annels i n the S ta nd-

ard, HRC, and IRC freq uency plans can be tuned with

these products. The VTS H6HZF1 h as an RCA in put

a nd is appropri ate fo r reception of signals modulated

in the PAL fo rma ts th at use a 5.5 MH z intercarri er. It

covers the 48.25 MHz to 855.25 MHz range. Other

variations of PLL tuners and off-air non-PLL tuners are

avai la bl e for a variety of destination c ountries.

MC44817D

Th e MC 448 17D i s a surface mou nt versi on o f the

MC44807P (DIP) PLL IC. It uses an 18-bi t serial da ta

string for configuring the PLL. The specification de-

fines a variety of possible operating configurations;

howe ver, the spec ifi c c ondi ti ons for these tuners will

be di scussed.

The computation for the required N-count to load

the PLL is ve ry simple.

N = FOSC / Step Size (1)

As indicated in Table 1, the step size is predeter-

mined for each application and is a constant in the

equation. The (1) indicates that it is equation 1 in this

document. The Voltage Controlled Oscillator (VCO)

output frequency term FOSC is determined by the output

from the PLL IC. FOSC is determined by:

OSC = FCHANNEL + FIF (2)

where FCHANNEL is the channel to whi ch you want to

tune, and F IF is the standard 45.75 MHz i nverted IF a s

referenced t o t h e video carrier. As an example of t h e

above expression, we wil l tune to Channe l 2, with the

video carrier at 55.25 MHz.

OSC = 55.25 M Hz + 45.75 MHz = 1 01 MHz (3)

The required VCO frequency to tune NTSC-M

Chan nel 2 , whi ch is at 55.25 MH z, referen ced to the

video carrier, is 101 MHz. The Intermediate Frequency

(IF) output for the NT SC tuners is 45.75 M Hz. As part

of the conversion process, the VCO is the conversion

Lo cal Oscillator (LO), and is tu ned above t he desired

frequency by an amount equal to the IF . Thus 101 MHz

– 55.25 MHz = 45.75 MHz produces the desired IF

outp ut frequency. For a given channel frequency, a d d

45.7 5 MH z, and the requi red VC O frequency wil l re-

sult.

Determine the N-count for the above channel by:

N = FOSC / Step S ize (1 )

N = 101 MHz / 62.5 k Hz = 1 616 (4)

The derived value of 1616 is the decimal value t hat

will be loaded into the PL L to set FOSC at 101 MHz. T he

maximum N-c ount al lowed i s 16,36 3 and a mi ni mu m

co unt of 17.

RF Appli cati on Note Page 1

F or the VTSH6 HZ F1, the same process is used to

tune to the lowest channel at 48.25 MHz, with the

standard IF placed at 38.9 MHz. Repeating from equa-

tio n s (2) and (1):

OSC = F CHANNEL + FIF (2)

OSC = 48.25 MHz + 38.9 MHz = 87.15 MHz (5)

N = FOSC / Step S i ze (1 )

N = 87.15 MHz / 50 k Hz = 1743 (6)

T o send this information to the PLL IC, it is combined

wi th 4 bits of Band Sw itch data. The PLL IC au tomat-

ically controls the three different tuning bands VHF

L ow, VH F H igh, and U HF b y respo ndi ng t o the Ba nd

Switch b its in the serial data st ring. The Band bits are

referenced in the separate tuning tables for each tuned

channe l and are provide d in each tuner specification.

To convert the N value t o the serial data string, the

Band bits occupy bits 1 through 4, and the N-value

occupi es the 14 remain ing bits of the serial string. F or

the example of the NTSC tuner , the derived value from

equation (4) of 1616 decimal must be con ver ted to 14

binary bits. The decimal value converts to a binary

value: 00011001010000. Please note that the l eading

00 have been added to complete the ful l 14-bit st ring.

It is essentia l t o make sure that the e ntire fourteen bits

ar e configured correctly.

T he Band S witch b it con figu ratio n fo r c han nel 2 i s

0 001. Thi s val ue is added t o the Mos t Si gn ifi can t Bi t

(MSB) en d of the d ata str ing. In t ab le f orm the proce ss

lo oks like:

DECIMAL BINARY

N-value 1616 011001010000

Add 2 bits 0 00011001010000

Band bits (4) 0001 000100011001010000

For the of the PAL tuner, the derived value from

equation (6) of 1743 decimal must be conver ted to 14

binary bits. The decimal value converts to a binary

va lu e: 000 110 11 001111 . P le ase no te th a t t h e l ea di ng

00 have been added to complete the ful l 14-bit st ring.

It is essentia l t o make sure that the e ntire fourteen bits

ar e configured correctly.

The Band Sw itch bi t c onfiguration for this cha nne l

is 0001. T h is val ue is ad ded to the Most Signific ant Bit

(MSB) en d of the d ata str ing. In t ab le f orm the proce ss

lo oks like:

DECIMAL BINARY

N-value 1743 011011001111

Ad d 2 bits 0 00011011001111

Band bit s (4 ) 0001 00010001101100 1111

P rogr amming Note

Care should be taken to ensure that extra clock

pulses are not present on the clock line prior to dis-

abling the Load Enable line on the PLL. Extraneous

clock pulses will create the appearance of the tuner

not ope ratin g correc tl y, a s it w il l tu ne errati call y. Th is

is due to t he dat a str eam be ing sh ift ed by one or more

addi ti onal bits, providi ng a division of all register val -

ues, and incorrect band switching control bits being

asserted.

Programming errors will create a wide variety of

problems that generate symptoms that are misleading.

If the circuit design appears to be correct in all re-

spec ts , an d di ffi cul ties are experience d, exami ne t he

timin g of the clock , data, and l oad enab le l ines c are-

full y. In addi ti on, insu re that the correct data bit s are

being sent to the PLL for your desired channel.

Band-Switching

The P LL IC prov id es four pins fo r c ontrol of band -

sw itching i n el ectron ic t uners. Diff erent sections of the

t uner are used for the VHF and UHF reception bands.

I n this manner, one sect io n of the tuner is enab led a nd

another section disabled for the specified tuning

range. This function is automatically controlled from

th e P LL IC di rectl y, as d eco ded by th e PLL from the

seria l tuni ng data string.

This function is transparent to the operator o f the

tuner module. The first four bits of t he serial data string

indicate which band is to be selected for operation.

Each tuner specification will indicate which band

selection is required for each channel in its tuning

r ange. The ba nd s wit ch range and associ ated b its are

shown in t he following tabl e. Band bit 3 activates the

EI A IS- 31 f ilter and d oes n ot affect the t uni ng perform-

ance . Bit 3 may be asserted at the same ti me as any

of the other three band bits. For ex ample:

CHA NNELS FRE QUENCIE S , MHZ BIT

PATTERN

2 – G 55.25 – 157.25 0001

H – W + 11 163.25 – 361.262 0010

W + 1 2 – W + 8 3 367.262 – 79 3.25 1000

TUNING TABLES

Tabl es wi th tu ni ng val ue s for N base d o n nomin al

VCO frequencies are avai lable on request. Standard

tuning frequencies are provided in most tuner specifi-

cations.

REFERENCES

V TSH6 UZ60, SHA RP Electron ics Corporation.

V TSH7 UZ50, SHA RP Electron ics Corporation.

V TSH6 HZF1, SHA RP El ectr on ics Corporation.

V TSH7 UF56, SHA RP Electron ics Corporation.

Internal-PLL Electronic Tuners VTSH Series

Page 2 RF Application Note