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| 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. FApplications FM intercom FM wireless microphone FSK modem FFeatures 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. FBlock diagram 108 Optical disc ICs FAbsolute maximum ratings (Ta = 25_C) BA7042 FRecommended operating conditions FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC=5.0V) 109 Optical disc ICs FMeasurement circuit BA7042 FApplication example 110 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. 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 V7)0.15) 102 [MHz] where C = C2)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. Temperature drift with a capacitor having a temperature coefficient of zero is *30kHz / _C when C = 25pF, fO = 14.3MHz, VCTL = 2.5V. (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. 111 Optical disc ICs FElectrical characteristic curves BA7042 FExternal dimensions (Units: mm) 112 |
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