How do I design the power supply rejection ratio of an RF amplifier bias circuit?
RF Amplifier PSRR Design
Power supply noise coupling is one of the most common causes of unexpected spurs and phase noise degradation in RF systems. Proper bias circuit PSRR design prevents these problems.
| Parameter | Class A | Class AB | Class F/Doherty |
|---|---|---|---|
| Max Efficiency | 50% | 50-78% | 70-90% |
| Linearity | Excellent | Good | Moderate (needs DPD) |
| P1dB Backoff | 0-3 dB | 3-6 dB | 6-10 dB |
| Complexity | Low | Low | High |
| Common Use | Test, small signal | General PA | Base station, broadcast |
Compression Behavior
When evaluating design the power supply rejection ratio of an rf amplifier bias circuit?, 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.
Efficiency Trade-offs
When evaluating design the power supply rejection ratio of an rf amplifier bias circuit?, 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
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Thermal Budget
When evaluating design the power supply rejection ratio of an rf amplifier bias circuit?, 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
What LDO should I use?
LDO selection for RF bias: key specifications: PSRR (look for greater than 60 dB at DC, greater than 40 dB at 100 kHz, greater than 20 dB at 1 MHz). Output noise (less than 10-50 μV RMS for low-noise applications). Dropout voltage (the minimum input-output voltage difference for regulation; lower is better for efficiency). Output current (must exceed the amplifier's DC current draw with margin). Recommended LDOs for RF: TI TPS7A47: 72 dB PSRR at 1 MHz, 4 μV RMS noise. Excellent for VCO and LNA bias. ADI LT3045: 76 dB PSRR at 1 MHz, 0.8 μV RMS noise. The lowest-noise LDO available. Ideal for phase-noise-sensitive applications. TI LP5907: 82 dB PSRR at 1 kHz, 6.5 μV RMS noise. Good general-purpose RF LDO.
What about switching converter noise?
Switching converters (buck, boost) generate significant noise at their switching frequency (typically 500 kHz-5 MHz) and harmonics. If a switching converter is used upstream: the LDO must have sufficient PSRR at the switching frequency to suppress the ripple. Additional LC filtering between the converter and the LDO is recommended. The switching converter output ripple is typically 10-50 mV peak-to-peak. With LDO PSRR of 40 dB at the switching frequency: the ripple is reduced to 0.1-0.5 mV. With additional ferrite+cap filtering: reduced to 10-50 μV (adequate for most RF amplifiers). For VCOs and frequency synthesizers: additional filtering may be needed to achieve less than 1 μV of supply ripple.
How do I verify PSRR?
PSRR verification: inject a known AC signal on the power supply (using a function generator in series with the supply) and measure the resulting modulation on the RF output (using a spectrum analyzer). Procedure: set the RF amplifier to its normal operating condition. Inject a low-level AC signal (10-50 mV RMS) on the supply at specific frequencies (100 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz). Measure the AM sidebands on the RF output using a spectrum analyzer. Calculate PSRR: PSRR = 20×log10(V_supply_AC / V_sideband_equivalent). This gives the actual end-to-end PSRR of the bias circuit including the LDO, filtering, and the amplifier's own internal PSRR.