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Device

Operating

Temperature Range

Package

MC1374

SEMICONDUCTOR

TECHNICAL DATA

TV MODULATOR CIRCUIT

ORDERING INFORMATION

MC1374P

TA = 0

to +70

Plastic DIP

Order this document by MC1374/D

P SUFFIX

PLASTIC PACKAGE

CASE 646

Figure 1. Simplified Application

Channel 3

R10

10k

470

5–25

MPN3404

0.001

+VCC = 12V

Output

Video In

Audio In

L1 – 4 Turns #22, 1/4

″

Dia.

L2 – 40 Turns, #36, 3/16

″

Dia.

VPin 11

VPin 1

Shaded Parts Optional

0.001

470

120

C14

0.01

2.2k

0.001

6.8k

3.3k

Ω

0.22

C15

0.001

C11

C12

C13

MC1374

C16

R14

56k

2.2k

1N914

C10

R11

220

R12

180k

R13

30k

560

MOTOROLA ANALOG IC DEVICE DATA

TV Modulator Circuit

The MC1374 includes an FM audio modulator, sound carrier oscillator, RF

oscillator, and RF dual input modulator. It is designed to generate a TV signal

from audio and video inputs. The MC1374’s wide dynamic range and low

distortion audio make it particularly well suited for applications such as video

tape recorders, video disc players, TV games and subscription decoders.

•

Single Supply, 5.0 V to 12 V

•

Channel 3 or 4 Operation

•

Variable Gain RF Modulator

•

Wide Dynamic Range

•

Low Intermodulation Distortion

•

Positive or Negative Sync

•

Low Audio Distortion

•

Few External Components

Motorola, Inc. 1996

Rev 0

MC1374

MOTOROLA ANALOG IC DEVICE DATA

MAXIMUM RATINGS

(TA = 25

C, unless otherwise noted.)

Rating

Value

Unit

Supply Voltage

Vdc

Operating Ambient Temperature Range

0 to +70

Storage Temperature Range

–65 to +150

Junction Temperature

150

Power Dissipation Package

Derate above 25

1.25

10 mW/

ELECTRICAL CHARACTERISTICS

(VCC = 12 Vdc, TA = 25

C, fc = 67.25 MHz, Figure 4 circuit, unless otherwise noted.)

Characteristics

Min

Typ

Max

Unit

AM OSCILLATOR/MODULATOR

Operating Supply Voltage

5.0

Supply Current (Figure 1)

–

Video Input Dynamic Range (Sync Amplitude)

0.25

1.0

V Pk

RF Output (Pin 9, R7 = 75

Ω

, No External Load)

–

170

–

mV pp

Carrier Suppression

–

Linearity (75% to 12.5% Carrier, 15 kHz to 3.58 MHz)

–

2.0

Differential Gain Distortion (IRE Test Signal)

5.0

7.0

Differential Phase Distortion (3.58 MHz IRE Test Signal)

–

1.5

2.0

Degrees

920 kHz Beat (3.58 MHz @ 30%, 4.5 MHz @ 25%)

–

–57

–

Video Bandwidth (75

Ω

Input Source)

–

MHz

Oscillator Frequency Range

–

105

–

MHz

Internal Resistance across Tank (Pin 6 to Pin 7)

Internal Capacitance across Tank (Pin 6 to Pin 7)

–

1.8

4.0

–

Ω

ELECTRICAL CHARACTERISTICS

(TA = 25

C, VCC = 12 Vdc, 4.5 MHz, Test circuit of Figure 11, unless otherwise noted.)

Characteristics

Min

Typ

Max

Unit

FM OSCILLATOR/MODULATOR

Frequency Range of Modulator

Frequency Shift versus Temperature (Pin 14 open)

Frequency Shift versus VCC (Pin 14 open)

Output Amplitude (Pin 3 not loaded)

Output Harmonics, Unmodulated

–

4.5

0.2

–

900

–

0.3

4.0

–

–40

MHz

kHz/

kHz/V

mVpp

Modulation Sensitivity

1.7 MHz

4.5 MHz

10.7 MHz

–

0.20

0.24

0.80

–

MHz/V

Audio Distortion (

25 kHz Deviation, Optimized Bias Pin 14)

Audio Distortion (

25 kHz Deviation, Pin 14 self biased)

Incidental AM (

25 kHz FM)

–

0.6

1.4

2.0

1.0

–

Audio Input Resistance (Pin 14 to ground)

Audio Input Capacitance (Pin 14 to ground)

–

6.0

5.0

–

Ω

Stray Tuning Capacitance (Pin 3 to ground)

Effective Oscillator Source Impedance (Pin 3 to load)

–

5.0

2.0

–

Ω

MC1374

MOTOROLA ANALOG IC DEVICE DATA

Figure 2. TV Modulator

Bias

Section

FM Oscillator/Modulator

Audio In

Sound Carrier

OSC B+

Sound Carrier

Oscillator

VCC

AM Modulator

RF Out

AM Oscillator

RF Tank

R10

R11

R12

6.0k

R16

R13

325

Q25

Q24

Q23

R15

R14

R17

Q12 Q13

Q14 Q15

Q21

Q22

Q10

Q11

Q26

Q27

Q16

Q17

Q18

Gnd

Sound Carrier

Gain

Video In

I = 1.15 mA 2

Q19 Q20

I = 1.15 mA 1

GENERAL INFORMATION

The MC1374 contains an RF oscillator, RF modulator, and

a phase shift type FM modulator, arranged to permit good

printed circuit layout of a complete TV modulation system.

The RF oscillator is similar to the one used in MC1373, and is

coupled internally in the same way. Its frequency is controlled

by an external tank on Pins 6 and 7, or by a crystal circuit, and

will operate to approximately 105 MHz. The video modulator

is a balanced type as used in the well known MC1496.

Modulated sound carrier and composite video information

can be put in separately on Pins 1 and 11 to minimize

unwanted crosstalk. A single resistor on Pins 12 and 13 is

selected to set the modulator gain. The RF output at Pin 9 is

a current source which drives a load connected from Pin 9 to

VCC.

The FM system was designed specifically for the TV

intercarrier function. For circuit economy, one phase shift

circuit was built into the ship. Still, it will operate from 1.4 MHz

to 14 MHz, low enough to be used in a cordless telephone

base station (1.76 MHz), and high enough to be used as an

FM IF test signal source (10.7 MHz). At 4.5 MHz, a deviation

25 kHz can be achieved with 0.6% distortion (typical).

In the circuit above, devices Q1 through Q7 are active in

the oscillator function. Differential amplifier Q3, Q4, Q5, and

Q6 acts as a gain stage, sinking current from input section

Q1, Q2 and the phase shift network R17, C1. Input amplifier

Q1, Q2 can vary the amount of “in phase” Q4 current to be

combined with phase shifter current in load resistor R16. The

R16 voltage is applied to emitter follower Q7 which drives an

external L–C circuit. Feedback from the center of the L–C

circuit back to the base of Q6 closes the loop. As audio input

is applied which would offset the stable oscillatory phase, the

frequency changes to counteract. The input to Pin 14 can

include a dc feedback current for AFC over a limited range.

The modulated FM signal from Pin 3 is coupled to Pin 1 of

the RF modulator and is then modulated onto the AM carrier.

MC1374

MOTOROLA ANALOG IC DEVICE DATA

AM Section

The AM modulator transfer function in Figure 3 shows that

the video input can be of either polarity (and can be applied at

either input). When the voltages on Pin 1 and Pin 11 are

equal, the RF output is theoretically zero. As the difference

between VPin 11 and VPin 1 increases, the RF output

increases linearly until all of the current from both I1 current

sources (Q8 and Q9) is flowing in one side of the modulator.

This occurs when

(VPin11 – VPin1) = I1 RG, where I1 is

typically 1.15 mA. The peak–to–peak RF output is the 2I1 RL.

Usually the value of RL is chosen to be 75

Ω

to ease the

design of the output filter and match into TV distribution

systems. The theoretical range of input voltage and RG is

quite wide, but noise and available sound level limit the useful

video (sync tip) amplitude to between 0.25 Vpk and 1.0 Vpk.

It is recommended that the value of RG be chosen so that

only about half of the dynamic range will be used at sync tip

level.

The operating window of Figure 5 shows a cross–hatched

area where Pin 1 and Pin 11 voltages must always be in order

to avoid saturation in any part of the modulator. The letter

represents one diode drop, or about 0.75 V. The oscillator

Pins 6 and 7 must be biased to a level of VCC –

– 2I1 RL (or

lower) and the input Pins 1 and 11 must always be at least 2

below that. It is permissible to operate down to 1.6 V,

saturating the current sources, but whenever possible, the

minimum should be 3

above ground.

The oscillator will operate dependably up to about

105 MHz with a broad range of tank circuit component

values. It is desirable to use a small L and a large C to

minimize the dependence on IC internal capacitance. An

operating Q between 10 and 20 is recommended. The values

of R1, R2 and R3 are chosen to produce the desired Q and to

set the Pin 6 and 7 dc voltage as discussed above.

Unbalanced operation, i.e., Pin 6 or 7 bypassed to ground, is

not recommended. Although the oscillator will still run, and

the modulator will produce a useable signal, this mode

causes substantial base–band video feedthrough.

Bandswitching, as Figure 1 shows, can still be accomplished

economically without using the unbalanced method.

The oscillator frequency with respect to temperature in the

test circuit shows less than

20 kHz total shift from 0

to 50

as shown in Figure 7. At higher temperatures the slope

approaches 2.0 kHz/

C. Improvement in this region would

require a temperature compensating tuning capacitor of the

N75 family.

Crystal control is feasible using the circuit shown in Figure

21. The crystal is a 3rd overtone series type, used in series

resonance. The L1, C2 resonance is adjusted well below the

crystal frequency and is sufficiently tolerant to permit fixed

values. A frequency shift versus temperature of less than

1.0 Hz/

C can be expected from this approach. The resistors

Ra and Rb are to suppress parasitic resonances.

Coupling of output RF to wiring and components on Pins 1

and 11 can cause as much as 300 kHz shift in carrier (at

67 MHz) over the video input range. A careful layout can

keep this shift below 10 kHz. Oscillator may also be

inadvertently coupled to the RF output, with the undesired

effect of preventing a good null when V11 = V1. Reasonable

care will yield carrier rejection ratios of 36 to 40 dB below sync

tip level carrier.

In television, one of the most serious concerns is the

prevention of the intermodulation of color (3.58 MHz) and

sound (4.5 MHz) frequencies, which causes a 920 kHz signal

to appear in the spectrum. Very little (3rd order) nonlinearity is

needed to cause this problem. The results in Figure 6 are

unsatisfactory, and demonstrate that too much of the

available dynamic range of the MC1374 has been used.

Figures 8 and 10 show that by either reducing standard

signal level, or reducing gain, acceptable results may be

obtained.

At VHF frequencies, small imbalances within the device

introduce substantial amounts of 2nd harmonic in the RF

output. At 67 MHz, the 2nd harmonic is only 6 to 8 dB below

the maximum fundamental. For this reason, a double pi low

pass filter is shown in the test circuit of Figure 3 and works

well for Channel 3 and 4 lab work. For a fully commercial

application, a vestigial sideband filter will be required. The

general form and approximate values are shown in Figure 19.

It must be exactly aligned to the particular channel.

2I1RL

–I1RG

+I1RG

Differential Input, V11–V1 (V)

RF Output

V(p–p)

Figure 3. AM Modulator Transfer Function

Figure 4. AM Test Circuit

470

0.001

VCC

C2 56

0.1

Video

Input

1.0k

V11

470

MC1374

MOTOROLA ANALOG IC DEVICE DATA

Figure 5. The Operating Window

Figure 6. 920 kHz Beat

Figure 7. RF Oscillator Frequency

versus Temperature

Figure 8. 920 kHz Beat

Figure 9. RF Oscillator Frequency

versus Supply Voltage

Figure 10. 920 kHz Beat

5.0

6.0

7.0

8.0

9.0

VCC

VCC, SUPPLY VOLTAGE (Vdc)

MODULA

INPUT

VOL

TAGE PIN 1 OR PIN 1

)

VCC – 2I1RL

VCC –

– 2I1RL

VCC – 3

– 2I1RL

Recommended

V1 & V11

Operating Region

Absolute Min = 1.6 V

+ Sat)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

DIFFERENTIAL INPUT (V11 – V1) [Vdc)

(fc

920 kHz)

AMPLITUDE

(fc) AMPLITUDE

[dB]

Initial Video = 1.0 Vdc

Chroma (3.58 MHz) = 300 mVpp

Sound (4.5 MHz) a) = 250 mVpp

b) = 500 mVpp

Gain Resistor RG = 1.0 k

Ω

100

TA, AMBIENT TEMPERATURE (

FREQUENCY

SHIFT

(kHz)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

DIFFERENTIAL INPUT (V11 – V1) [Vdc)

(fc) AMPLITUDE

[dB]

Initial Video = 0.5 Vdc

Chroma (3.58 MHz) = 150 mVpp

Sound (4.5 MHz) a) = 125 mVpp

b) = 250 mVpp

Gain Resistor RG = 1.0 k

Ω

5.0

6.0

7.0

8.0

9.0

VCC, SUPPLY VOLTAGE (V)

NORMALIZED FREQUENCY

(kHz)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.5 1.6 1.8 2.0 2.2 2.4 2.8

DIFFERENTIAL INPUT (V11 – V1) [Vdc)

[dB]

Initial Video = 1.0 Vdc

Chroma (3.58 MHz) = 300 mVpp

Sound (4.5 MHz) a) = 250 mVpp

b) = 500 mVpp

Gain Resistor (RG) = 2.2 k

Ω

RL = 75

Ω

I1 = 1.15 mA

(fc

920 kHz)

AMPLITUDE

(fc

920 kHz)

AMPLITUDE

(fc) AMPLITUDE

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

–10

–20

–30

–40

–50

–60

–70

–80

–10

–20

–30

–40

–50

–60

–70

–10

–20

–30

–40

–50

–60

–70

–80

–10

–20

–30

–40

–50

–60

–70

–10

–20

–30

–40

–50

–60

–70

–80

TA = 25

fc = 61.25 MHz

≈

61.25 MHz

VCC = 12 Vdc

MC1374

MOTOROLA ANALOG IC DEVICE DATA

FM Section

The oscillator center is approximately the resonance of the

inductor L2 from Pin 2 to Pin 3 and the effective capacitance

C3 from Pin 3 to ground. For overall oscillator stability, it is

best to keep XL in the range of 300

Ω

to 1.0 k

Ω

The modulator transfer characteristic at 4.5 MHz is shown

in Figure 15. Transfer curves at other frequencies have a very

similar shape, but differ in deviation per input volt, as shown in

Figures 13 and 17.

Most applications will not require DC connection to the

audio input, Pin 14. However, some improvements can be

achieved by the addition of biasing circuitry. The unaided

device will establish its own Pin 14 bias at 4

, or about 3.0 V.

This bias is a little too high for optimum modulation linearity.

Figure 14 shows better than 2 to 1 improvement in distortion

between the unaided device and pulling Pin 14 down to 2.6 V

to 2.7 V. This can be accomplished by a simple divider, if the

supply voltage is relatively constant.

The impedance of the divider has a bearing on the

frequency versus temperature stability of the FM system. A

divider of 180 k

Ω

and 30 k

Ω

(for VCC = 12 V) will give good

temperature stabilization results. However, as Figure 18

shows, a divider is not a good method if the supply voltage

varies. The designer must make the decisions here, based

on considerations of economy, distortion and temperature

requirements and power supply capability. If the distortion

requirements are not stringent, then no bias components are

needed. If, in this case, the temperature compensation needs

to be improved in the high ambient area, the tuning capacitor

from Pin 3 to ground can be selected from N75 or N150

temperature compensation types.

Another reason for DC input to Pin 14 is the possibility of

automatic frequency control. Where high accuracy of

inter–carrier frequency is required, it may be desirable to feed

back the DC output of an AFC or phase detector for nominal

carrier frequency control. Only limited control range could be

used without adversely affecting the distortion performance,

but very little frequency compensation will be needed.

One added convenience in the FM section is the separate

Pin “oscillator B+” which permits disabling of the sound

system during alignment of the AM section. Usually it can be

hard wired to the VCC source without decoupling.

Standard practice in television is to provide pre–emphasis

of higher audio frequencies at the transmitter and a matching

de–emphasis in the TV receiver audio amplifier. The purpose

of this is to counteract the fact that less energy is usually

present in the higher frequencies, and also that fewer

modulation sidebands are within the deviation window. Both

factors degrade signal to noise ration. Pre–emphasis of 75

is standard practice. For cases where it has not been

provided, a suitable pre–emphasis network is covered in

Figure 20.

It would seem natural to take the FM system output from

Pin 2, the emitter follower output, but this output is high in

harmonic content. Taking the output from Pin 3 sacrifices

somewhat in source impedance but results in a clean output

fundamental, with all harmonics more than 40 dB down. This

choice removes the need for additional filtering components.

The source impedance of Pin 3 is approximately 2.0 k

Ω

, and

the open circuit amplitude is about 900 mV pp for the test

circuit shown in Figure 11.

T h e a p p l i c a t i o n c i r c u i t o f F i g u r e 1 s h o w s t h e

recommended approach to coupling the FM output from Pin 3

to the AM modulator input, Pin 1. The input impedance at Pin

1 is very high, so the intercarrier level is determined by the

source impedance of Pin 3 driving through C4 into the video

bias circuit impedance of R4 and R5, about 2.2 k. This

provides an intercarrier level of 500 mV pp, which is correct

for the 1.0 V peak video level chosen in this design. Resistor

R6 and the input capacitance of Pin 1 provide some

decoupling of stray pickup of RF oscillator or AM output which

may be coupled to the sound circuitry.

(pF)

(MHz)

(µ

10.7

4.5

120

200

1.76

VCC

C14

0.01

Intercarrier

Sound Output

(Use FET Probe)

120pF

0.001

R12

R13

Audio

Input

Optional Bias R

(See Text)

Figure 11. FM Test Circuit

1.4

2.0

3.0

5.0

4.0

6.0 7.0 8.0 9.0 10

fosc, OSCILLATOR FREQUENCY [MHz]

MAXIMUM CENTER-FREQUENCY

SLOPE ( f/ V ) (MHz/V)

∆∆

TA = 25

Figure 12. Modulator Sensitivity

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

MC1374

MOTOROLA ANALOG IC DEVICE DATA

f osc

, OSCILLA

FREQUENCY

(MHz)

Figure 13. Modulator Transfer Function

Figure 14. Distortion versus Modulation Depth

Figure 15. Modulator Transfer Function

Figure 16. FM System Frequency

versus Temperature

Figure 17. Modulator Transfer Function

Figure 18. FM System Frequency versus VCC

4.0

5.0

6.0

7.0

8.0

9.0

VCC, SUPPLY VOLTAGE (Vdc)

1.0

2.0

3.0

4.0

5.0

6.0

7.0

DC INPUT VOLTAGE, PIN 14 (V)

1.0

2.0

3.0

4.0

5.0

6.0

7.0

DC INPUT VOLTAGE, PIN 14 (V)

1.0

2.0

3.0

4.0

5.0

6.0

7.0

DC INPUT VOLTAGE, PIN 14 (V)

12 V

9.0 V VCC

5.0 V

100

DEVIATION (kHz)

DIST

TION (%)

VCC = 12 V

TA = 25

fc = 4.5 MHz

100

TA, AMBIENT TEMPERATURE (

f, FREQUENCY

(MHz)

f, FREQUENCY

(MHz)

osc

, OSCILLA

FREQUENCY

(MHz)

f osc

, OSCILLA

FREQUENCY

(MHz)

2.1

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

5.0

4.0

3.0

2.0

1.0

4.9

4.8

4.7

4.6

4.5

4.4

4.3

4.2

4.1

4.55

4.54

4.53

4.52

4.51

4.50

4.49

4.48

4.47

11.6

11.2

11.0

10.6

10.4

10.2

10.0

9.8

9.6

10.8

11.4

4.50

4.49

4.48

4.47

4.46

4.45

4.44

4.43

4.42

TA = 25

(1.76 MHz)

VCC = 12 V

VCC = 5.0 V, 9.0 V

Self Bias (2.9–3.0 V)

Optimum Bias (2.6–2.7 V)

TA = 25

(4.5 MHz)

VCC = 12 V

VCC = 5.0 V, 9.0 V

VCC = 12 V

Pin 14 V to 2.6 V

180 k/30 k Divider<