ROHM BA7042

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.
Block diagram
108
4) Maximum oscillation frequency of 18MHz.
5) DIP 8-pin package.
Optical disc ICs
BA7042
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC=5.0V)
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Optical disc ICs
Measurement circuit
Application example
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BA7042
Optical disc ICs
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 VCC / 2. The amplification
degree is determined by the external constant.
FOperation notes
(1) Temperature drift of the oscillator circuit can be reduced by configuring with a capacitor having a temperature coefficient. Temperature drift with a capacitor having
a temperature coefficient of zero is 30kHz / _C when
C = 25pF, fO = 14.3MHz, VCTL = 2.5V.
BA7042
(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 :
f
1
C (pF)
(1.3 V70.15) 102 [MHz]
where C = C2C3, 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.
(2) The control amplifier’s frequency characteristics
depend on NF. When used as a reversing amplifier, cutoff
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
Electrical characteristic curves
External dimensions (Units: mm)
112
BA7042