Low-Power Voltage-Controlled Oscillator Buffer: MC12149

The ML12149 is intended for applications requiring high frequency signal generation up to 1300 MHz. An external tank circuit is used to determine the desired frequency of operation. The VCO is realized using an emmiter–coupled pair topology. The ML12149 can be used with an emitter PLL IC such as the Motorola ML12210 1.1 GHz Frequency Synthesizer to realize a complete PLL sub–system. The device is specified to operate over a voltage supply range of 2.7 to 5.5 V. It has a typical current consumption of 15 mA at 3.0 V which makes it attractive for battery operated handheld systems.

• Operated Up to 1.3 GHz
• Space–Efficient 8–Pin SOIC Package
• Low Power 15 mA Typical @ 3.0 V Operation
• Supply Voltage of 2.7 to 5.5 V
• Typical 900 MHz Performance
• Phase Noise – 105 dBc/Hz @ 100 Khz Offset
• Tuning Voltage Sensitivity of 20 MHz/V
• Output Amplitude Adjustment Capability
• Two High Drive Output with an Adjustable Range from
• 8.0 to –2.0 dBm
• One Low–Drive Output for Interfacing to a Prescaler
• Operating Temperature Range TA = –40 to 85°C

The device has three high frequency outputs which make it attractive for transceiver applications which require both a transmit and receive local oscillator (LO) signal as well as a lower amplitude signal to drive the prescaler input of the frequency synthesizer. The outputs Q and QB are available for servicing the receiver IF and transmitter up–converter single–ended. In receiver applications, the outputs can be used together if it is necessary to generate a differential signal for the receiver IF. Because the Q and QB outputs are open collector, terminations to the VCC supply are required for proper operation. Since the outputs are complementary, both outputs must be terminated even if only one is needed. The Q and QB outputs have a nominal drive level of –8dBm to conserve power. A level adjustment pin (CNTL) is available, which when tied to ground, boosts the nominal output levels to –2.0 dBm. A low power VCO output (Q2) is also provided to drive the prescaler input of the PLL. The amplitude of this signal is nominally 500 mV which is suitable for most prescalers. External components required for the ML12149 are: (1) tank circuit (LC network); (2) Inductor/capacitor to provide the termination for the open collector outputs; and (3) adequate supply voltage bypassing. The tank circuit consists of a high–Q inductor and varactor components. The preferred tank configuration allows the user to tune the VCO across the full supply range. VCO performance such as center frequency, tuning voltage sensitivity, and noise characteristics are dependent on the particular components and configuration of the VCO tank circuit.