The performance indicators of frequency synthesizers are crucial to evaluating their applicability and performance in various applications. The following are some of the main performance indicators:

1. Frequency Range:

Refers to the range between the lowest and highest frequencies that a frequency synthesizer can generate. For example, the frequency range of some frequency synthesizers may be 100kHz to 100MHz, while frequency synthesizers used for RF communications may cover a range of hundreds of MHz to tens of GHz. A wider frequency range can make frequency synthesizers suitable for more different application scenarios. For example, in communication systems, when multiple frequency bands need to be covered, the frequency synthesizer is required to have a sufficiently wide frequency range.

2. Frequency Resolution:

Indicates the minimum frequency interval that a frequency synthesizer can generate, that is, the minimum frequency change that can be accurately adjusted. For example, a frequency synthesizer with a frequency resolution of 1Hz can generate frequencies with precise intervals such as 1000Hz, 1001Hz, and 1002Hz. High frequency resolution is very important for applications that require precise frequency control, such as in spectrum analysis, precision measurement, and other fields.

3. Frequency Stability:

Measures the ability of the frequency synthesizer output frequency to remain stable over time, temperature, power supply voltage and other factors. It can be subdivided into long-term stability, short-term stability, temperature stability and voltage stability, etc.:

• Long-Term Stability:

Usually expressed as the frequency change within a certain period of time (such as one day, one month, one year), in units of ppm (parts per million) or ppb (parts per billion). For example, a long-term stability of ±1ppm/year means that the output frequency of the frequency synthesizer does not change by more than ±1ppm in one year.

• Short-Term Stability:

Generally, the focus is on the frequency fluctuation within a shorter period of time (such as 1 second, 1 millisecond), and the Allan variance is often used to describe it. Short-term stability is very critical for some applications with high real-time requirements, such as clock signal generation in digital communications.

• Temperature Stability:

Reflects the degree to which the output frequency of the frequency synthesizer changes with temperature, in units of ppm/℃. Temperature changes can affect the performance of components in the frequency synthesizer, such as the frequency of the crystal oscillator will change with temperature, so temperature stability is an important indicator.

• Voltage Stability:

Indicates the variation of output frequency with power supply voltage, in ppm/V. Fluctuation of power supply voltage may cause the output frequency of frequency synthesizer to change, and good voltage stability can reduce this effect.

4. Phase Noise:

It is used to describe the phase jitter of the output signal of frequency synthesizer, and is one of the important indicators to measure signal quality. The lower the phase noise, the higher the purity of the signal and the smaller the impact on the subsequent circuit. It is usually expressed in dBc/Hz, which refers to the ratio of noise power to signal power at a certain frequency offset. For example, at a frequency offset of 10kHz, the phase noise is -100dBc/Hz, which means that at this frequency offset, the noise power is 100dB lower than the signal power. In communication systems, high phase noise may cause signal demodulation errors and reduce communication quality.

5. Spurious Suppression:

Spurious refers to other frequency components in the output signal of frequency synthesizer except the desired frequency components. Spurious suppression indicates the ability of frequency synthesizer to suppress these spurious signals, usually expressed in dBc. For example, a spurious suppression of -60dBc means that the power of the spurious signal is 60dB lower than the main signal power. Good spurious suppression can reduce the interference of spurious signals to other devices or systems and improve the reliability of the system.

6. Frequency Conversion Time:

Refers to the time required for the frequency synthesizer to switch from one frequency to another and achieve a stable output. In some applications that require fast frequency switching, such as frequency hopping communication systems, frequency conversion time is a key indicator. Shorter frequency conversion time can enable the system to adapt to different communication needs more quickly and improve the flexibility and anti-interference ability of the system.

7. Output Power:

Refers to the power of the output signal of the frequency synthesizer, usually in dBm or mW. Appropriate output power is important to ensure the transmission distance and quality of the signal. In some applications, the output power of the frequency synthesizer needs to be adjusted according to the requirements of the subsequent circuit to ensure that the signal can be received and processed correctly.