Datasheet BA7042 Datasheet (ROHM)

Optical disc ICs

VCO with sensitivity adjustment
function

BA7042

The BA7042 is a monolithic IC comprising a VCO (voltage controlled oscillator) with sensitivity adjusting capabilities.
The oscillation frequency can be set with an external constant, and is controlled according to the control voltage. The
BA7042 can be used to produce high-modulation-factor FM signals by superimposing its control voltage with AC signals,
and to configure a PLL circuit just by attaching a frequency divider and a phase comparator.

Applications
FM intercom
FM wireless microphone
FSK modem

Features

1) The number of external components is minimized.

2) Internal control amplifier for the VCO.

3) Oscillation frequency can be set with an external
constant.

4) Maximum oscillation frequency of 18MHz.

5) DIP 8-pin package.

Block diagram

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Optical disc ICs BA7042

FAbsolute maximum ratings (Ta = 25_C)

FRecommended operating conditions

FElectrical characteristics (unless otherwise noted, Ta = 25_C, V

CC=5.0V)

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Optical disc ICs BA7042

Measurement circuit

Application example

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Optical disc ICs BA7042

FCircuit operation
(1) Circuit configuration
The control voltage, input through pin 1, is amplified by
the control amplifier, then output to pin 7 and input to the
VCO control circuit. The oscillation frequency of the VCO
is determined by the attached capacitor and controlled
according to the control voltage. Highly modulated FM
signals can be produced by superimposing the control
voltage with AC signals.
(2) Block description

(1) Control amplifier (pin 1, pin 7, pin 8)

The differential amplifier’s positive input is pin 1, its nega­tive input pin 8, and its output pin 7. Set the input bias volt­age so that the pin 7 voltage is V

CC/2. The amplification

degree is determined by the external constant.

(2) VCO (pin 2, pin 3, pin 5)

The oscillator’s center frequency is set with an external
capacitor. Use the following equation to calculate oscilla­tion frequency :

1

f

C (pF)

where C = C

 (1.3  V70.15)  102 [MHz]

2C3, V7 = pin 7 voltage

The oscillation frequency set by the capacitor is the cen­ter frequency in the VCO’s frequency variation range.
The VCO can be given a roughly linear oscillation fre­quency by changing its control voltage.

FOperation notes
(1) Temperature drift of the oscillator circuit can be re­duced by configuring with a capacitor having a tempera­ture coefficient. T emperature drift with a capacitor having
a temperature coefficient of zero is 30kHz / _C when
C = 25pF, f

O = 14.3MHz, VCTL = 2.5V.

(2) The control amplifier’s frequency characteristics
depend on NF . When used as a reversing amplifier, cutof f
frequency is roughly 100kHz with a gain of 20dB. When
configuring PLL circuits, remember that loop stability is
affected by the amplifier’s frequency characteristics.

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Optical disc ICs BA7042

Electrical characteristic curves

External dimensions (Units: mm)

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