What is the difference between a single balanced and a double balanced mixer in terms of spurious performance?
Balanced Mixer Types
Mixer balance refers to the symmetry of the diode configuration and its effect on suppressing unwanted mixing products. An unbalanced (single-ended) mixer has no inherent spurious suppression and produces all possible m×fLO ± n×fRF mixing products at the IF port. Each level of balance adds a degree of spurious suppression.
| 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 |
Frequently Asked Questions
How much spur suppression?
Single-balanced: 20-35 dB suppression of even-order products of the balanced port. Double-balanced: 30-50 dB suppression of all even-order products. The actual suppression depends on the balance (amplitude and phase matching between diodes and balun arms).
What about triple-balanced mixers?
Triple-balanced mixers use two double-balanced mixer rings and additional transformers, providing isolation and spurious suppression on all three ports simultaneously. They achieve the widest bandwidth (multi-octave on all ports) but have higher conversion loss (8-10 dB) and require more LO power.
When is single-balanced sufficient?
When the simplified spurious spectrum is acceptable and cost/size are priorities. Single-balanced mixers are smaller, require less LO power (3 dB less than DBM), and are easier to integrate at mmWave frequencies where four-diode ring configurations become impractical.