Mixer Conversion Loss
Understanding Mixer Conversion Loss
Conversion loss is the primary specification of a passive mixer. It determines how much the signal is attenuated during frequency conversion and directly impacts the receiver's noise figure and sensitivity.
Conversion Loss by Mixer Type
| Mixer Type | Conversion Loss | LO Drive |
|---|---|---|
| Single-ended | 6-9 dB | +7 dBm |
| Single-balanced | 6-8 dB | +7 to +10 dBm |
| Double-balanced | 5-8 dB | +7 to +17 dBm |
| 2nd harmonic | 10-15 dB | +10 to +17 dBm |
| Active (Gilbert cell) | -5 to +5 (gain) | Variable |
Factors Affecting Conversion Loss
- LO drive level: Insufficient LO power increases conversion loss. Each mixer has an optimum LO drive level.
- Frequency: Conversion loss increases at higher frequencies due to parasitic reactances.
- IF frequency: Far from the RF, conversion loss is relatively constant. Near DC, video impedance effects matter.
Frequently Asked Questions
What is mixer conversion loss?
Conversion loss is the ratio of IF output to RF input power. Passive mixers have 5-8 dB conversion loss. Active mixers can have conversion gain. Conversion loss directly adds to receiver noise figure.
How does conversion loss affect noise figure?
For a passive mixer, NF approximately equals the conversion loss. An 8 dB conversion loss mixer has approximately 8 dB NF. This is why an LNA before the mixer (with 1-2 dB NF and 15-20 dB gain) is essential to set the system NF.
Can you reduce conversion loss?
Ensure adequate LO drive level (check datasheet). Use the correct LO frequency range. Proper impedance terminations at all ports (RF, LO, IF). Active mixers provide conversion gain but have limited dynamic range.