What is the phase noise degradation of a signal through a frequency multiplier chain?
Frequency Multiplication Phase Noise
Phase noise scaling through frequency multiplication is one of the most important relationships in synthesizer design. It determines the optimal approach for generating low-phase-noise signals at microwave and mmW frequencies.
| Parameter | Passive Diode | Active FET | Subharmonic |
|---|---|---|---|
| Conversion Loss/Gain | 5-9 dB loss | 0-10 dB gain | 8-12 dB loss |
| LO Drive Level | +7 to +17 dBm | -5 to +5 dBm | +5 to +13 dBm |
| IP3 (typical) | +15 to +30 dBm | +5 to +20 dBm | +10 to +20 dBm |
| Noise Figure | 5-9 dB (= conv. loss) | 8-15 dB | 9-14 dB |
| LO-RF Isolation | 25-45 dB | 15-35 dB | 20-40 dB |
Conversion Architecture
When evaluating the phase noise degradation of a signal through a frequency multiplier chain?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Spurious Performance
When evaluating the phase noise degradation of a signal through a frequency multiplier chain?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
Frequently Asked Questions
Does this apply to PLL-based synthesis?
Within the PLL loop bandwidth: yes. The reference phase noise is multiplied by 20×log10(N) where N is the total division ratio. This is because the PLL forces the VCO to track the reference × N, including the reference's phase deviations × N. Outside the loop bandwidth: the VCO's own phase noise dominates (the PLL no longer controls the VCO). This is why PLL synthesizer design involves selecting the loop bandwidth: narrow bandwidth reduces the multiplied reference noise (at far offsets) but allows more VCO noise (at close offsets). The loop bandwidth is typically set where the multiplied reference noise equals the VCO noise.
Is there a way to avoid the 20logN penalty?
No. The 20×log10(N) phase noise increase is a fundamental physical consequence of frequency multiplication. However: the penalty can be managed by: starting with the lowest-phase-noise source available (high-quality crystal oscillators, sapphire oscillators, or optical references), using the minimum multiplication factor (prefer direct high-frequency oscillators when their phase noise is comparable to the multiplied alternative), and using offset locking or injection locking (an indirect method that transfers the spectral purity of a reference to a high-frequency oscillator without formal multiplication).
What about frequency division?
Frequency division by N improves the phase noise by 20×log10(N) dB (the inverse of multiplication). This is why low-phase-noise mmW sources sometimes use a high-frequency oscillator divided down: a 40 GHz oscillator divided by 4 to 10 GHz has 12 dB lower phase noise at 10 GHz than the original oscillator at 40 GHz. Division also reduces the spurious content of the signal.