Modulator Functionality

MOTOROLA

MC44BC375/U/J/T Technical Data

11

12 Modulator Functionality

12.1 Power Supply

The two device Vccs (pins 11 and 14) must be applied at the same time to ensure all internal blocks are

correctly biased. All other pins must not be biased before Vcc is applied to device.

Video Black Level

Audio signal: 1Khz, 205mVrms.

This is measured using a Rohde &

Schwarz AMFS Demodulator in B/G and

a HP8903A Audio Analyzer at 1kHz

The audio signal 205mV at 1kHz is supplied by the Audio Analyzer, and

the FM demodulated signal deviation is indicated on the Demodulator in

Khz peak.

This value is then converted in% of FM deviation, based on specified

standards.

Audio Frequency response

Video Black Level

This is measured using a Rohde &

Schwarz AMFS Demodulator in B/G and

a HP8903A.

demodulated by the Demodulator and the audio analyzer measures the

AC amplitude of this demodulated audio signal: this value is taken as a

reference (0dB).

The audio signal is then swept from 50Hz to 15KHz, and demodulated

AC amplitude is measured in dB relative to the 1KHz reference.

Audio pre-emphasis and de-emphasis circuits are engaged, all audio

analyzer filters are switched OFF.

Audio Distortion FM

Audio: 1Khz, adjustable level

Video Black Level

This is measured using a Rohde &

Schwarz AMFS UHF Demodulator in B/G

and a HP8903A Audio Analyzer at 1kHz.

The output level of the Audio analyzer is

varied to obtain a deviation of 50kHz

indicated on the Demodulator.

The input rms detector of the Audio Analyzer converts the ac level of the

combined signal + noise + distortion to dc. It then removes the

fundamental signal (1kHz) after having measured the frequency. The

output rms detector converts the residual noise + distortion to dc. The dc

voltmeter measures both dc signals and calculates the ratio in% of the

two signals.

AudioSignal toNoise

Audio: 1Khz, adjustable level

Video: EBU Color Bars

This is measured using a Rohde &

Schwarz AMFS Demodulator in B/G and

a HP8903A Audio Analyzer at 1kHz. The

output level of the Audio analyzer is

varied to obtain a Modulation Deviation

of 25kHz indicated on the AMFS

Demodulator.

The Audio Analyzer alternately turns ON and OFF it's internal audio

source to make a measure of the Audio signal plus noise and then

another measure of only the noise.

The measurement is made using the internal CCIR468-2 Filter of the

Audio Analyzer together with the internal 30+/-2kHz (60dB/decade)

Lowpass filters.

The AMFS demodulator uses a quasi-parallel demodulation as is the

case in a normal TV set. In this mode the Nyquist filter is bypassed and

the video carrier is used without added delay to effectuate intercarrier

conversion. In this mode the phase noise information fully cancels out

and the true S/N can be measured

Device and Signals Set-up

Measurement Set-up

ADist

Distorsion

Noise

+

() Distorsion Noise Signal

++

()

⁄

=

ASN dB

()

20

Signal

Noise

+

() Noise

()

⁄

log

×

=

Freescale Semiconductor, Inc.

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Go to: www.freescale.com