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Mixer Design Calculator
Complete mixer design tool — IF frequency, image frequency, half-IF spur, conversion gain, IIP3, SSB/DSB noise figure, IF filter specification and a full m×fRF ± n×fLO spur table up to order 5.
Mixer Specifications
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Mixer Topology
Down-conversion (RX):
fIF = |fRF − fLO| → Low-side: fLO = fRF − fIF
Image: fim = fLO − fIF (low-side) = fRF − 2·fIF
Half-IF spur: fRF ± fIF/2 mixes to fIF/2 via 2nd-order products
Spur: m×fRF − n×fLO = fIF
(1,1) = desired signal | (2,2) = half-IF | (1,3),(3,2) = common problems
SSB NF: Total NF = NFSSB (image noise folds in)
DSB NF: NFDSB = NFSSB − 3 dB (image band used)
fIF = |fRF − fLO| → Low-side: fLO = fRF − fIF
Image: fim = fLO − fIF (low-side) = fRF − 2·fIF
Half-IF spur: fRF ± fIF/2 mixes to fIF/2 via 2nd-order products
Spur: m×fRF − n×fLO = fIF
(1,1) = desired signal | (2,2) = half-IF | (1,3),(3,2) = common problems
SSB NF: Total NF = NFSSB (image noise folds in)
DSB NF: NFDSB = NFSSB − 3 dB (image band used)
Half-IF spur rule: A blocker at fRF±fIF/2 creates an in-band spur via the 2nd-order term (IM2). For good IM2, the IP2 should be ≥50 dBm. Direct conversion (fIF=0) eliminates the image problem but suffers worst-case from DC offset, flicker noise and IM2.
Frequency Plan Results
Frequency Plan
LO frequency fLO—
IF frequency fIF—
Image frequency fIM—
Image separation from fRF—
Half-IF spur frequency—
IF filter centre frequency—
IF filter bandwidth needed—
Image rejection required—
Mixer Performance
OIP3 (output-referred)—
DSB noise figure NFDSB—
LO leakage to RF port—
LO leakage to IF port—
RF feedthrough to IF—
Spur Table — m×fRF ± n×fLO products
| m | n | fspur (MHz) | In-band? | Relative level |
|---|
Highlighted rows fall within IF bandwidth — require pre-selection filtering or image rejection.