Using VCO to achieve direct frequency modulation of varactor diode 6

--From the previous analysis, it can be seen that the phase-locked loop is a narrowband carrier tracking loop, so bl should be less than the modulation frequency of 30Hz. Therefore, the parameters r1, r2, and c of the loop filter should be adjusted to make bl less than 30Hz. Taking ξ=0.7,diode  let bl=10Hz, n=10000, c=10 μ f, kv=2 π× 1.2 × 106 (rad/v) ≈ 7.54 × 106 (rad/v), then according to the formula, r1=170k ω, r2=7.5k ω can be obtained. The design and testing results of PCB boards - frequency synthesizers have strict requirements for electromagnetic compatibility issues such as power supply and ground wire distribution. This is because the noise from the power supply and data bus can couple into the phase-locked loop system, causing phase noise and spurious interference to deteriorate. Therefore, when laying out PCB layouts,diode  the following points should be achieved. ---(1) The phase detector and voltage controlled oscillator are separately powered and stabilized, and the input and output terminals of the voltage regulator are connected with π - type filtering circuits; ---(2) Wiring and component arrangement should be as neat as possible; ---(3) The power line should be widened to about 1mm, and the signal line width should also reach 0.75mm. Taking the above measures can effectively filter out all useless frequencies and power ripple, suppress various interferences and noise,diode  and reduce the phase noise and spurious of the frequency synthesizer. Tables 1 and 2 below provide various test indicators at a carrier frequency of 100mhz, while Table 3 presents the frequency modulation signal-to-noise ratio indicators of the circuit at each carrier frequency point. ---From the data in the table, it can be seen that this circuit fully meets the requirements of the system and has good characteristics in terms of phase noise, nonlinear distortion, audio frequency response, diode and frequency modulation signal-to-noise ratio. The phase noise is less than -100dB/Hz/10kHz, the nonlinear distortion is less than 0.1%, the audio frequency response is very ideal, diode and the frequency modulation signal-to-noise ratio reaches over 80dB. At the same time, the carrier frequency stability is controlled within 200Hz, and the output signal frequency deviation does not exceed 1kHz. All indicators meet the technical requirements of the State Administration of Radio, Film and Television. Moreover, this circuit has a small debugging volume, low cost, and is easier to mass produce diode