The figure below illustrates an actual frequency synthesizer built using the Q2230 excitation phase-locked frequency multiplier system. The system operates with a 40 MHz reference clock, enabling it to generate a sine wave with a resolution of 0.01 Hz from DC up to 15 MHz and a peak-to-peak voltage of 10 V. Its spectral purity exceeds 70 dB, and it can also output TTL signals across a wide range—from DC to 60 MHz—with support for AM, FM, FSK, and DPSK modulation.
1. **40 MHz High Stability Reference Clock**
To ensure high-quality signal output, the 40 MHz system clock is derived from an 8th-order PLL system that uses a 5 MHz constant temperature crystal oscillator (with stability better than 10â»â¹/s). This PLL includes a 40 MHz crystal oscillator as its VCO, ensuring excellent spectral purity and frequency stability for the entire system.
2. **Microprocessor Control System**
At the heart of the system is an 8031-based microprocessor control unit, which includes a keyboard display, serial communication port, and CPU module. It manages various functions such as modulation control (FM, FSK, DPSK), amplitude control via a DAC, DC offset adjustment, level comparison, and output switching. It also handles panel functions and display control, making the system highly user-friendly and versatile.
3. **TTL Comparator**
TTL Comparator A is responsible for generating a DC to 15 MHz TTL-level output. Meanwhile, the output from TTL Comparator B is fed back to the CPU unit and the level comparison DAC, allowing precise control over the amplitude of the sinusoidal output, ensuring accuracy and consistency.
4. **15–60 MHz PLL System**
This section covers a 4x phase-locked loop system operating in the 15–60 MHz range. By using switching controls, the system can provide TTL signals from DC up to 60 MHz at the TTL output, expanding the synthesizer’s versatility for a wide range of applications.
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