TRF1305A1: Noise density

Hello Ion,

Yes — the TRF1305A1 is a worthwhile noise upgrade over the LMH5401

The TRF1305A1 delivers meaningfully lower noise than the LMH5401 across the board. Its input-referred spot noise is approximately 1.08 nV/√Hz compared to the LMH5401's 1.35 nV/√Hz (both including external resistor contributions at their typical gain settings) . The noise figure tells the same story: at 500 MHz with a 50Ω source in single-ended-to-differential mode, the TRF1305A1 achieves 7.2 dB NF versus the LMH5401's 9.6 dB, a 2.4 dB improvement that holds across frequency (8.3 dB vs ~10 dB at 1 GHz, 8.9 dB vs ~11 dB at 2 GHz). This means the TRF1305A1 adds substantially less noise to your signal chain relative to the source.

The TRF1305 family comes in three fixed-gain variants that are pin-compatible with each other: the A1 (15 dB), B1 (10 dB), and C1 (5 dB). For noise figure, the A1 is best at 7.2 dB, the B1 is next at 8.0 dB, and the C1 trails at 11.3 dB (all at 500 MHz, D2D) — as expected, since higher gain yields better NF. However, for absolute output noise spectral density, the ranking reverses: the C1 is lowest at –157.5 dBm/Hz, followed by the B1 at –156.2 dBm/Hz, and the A1 at –152 dBm/Hz, because less gain means less amplified noise at the output. All three variants beat the LMH5401 on noise figure. The B1 at 10 dB gain is the closest fit to a typical LMH5401 design running at 12 dB, still offering ~1.6 dB better NF while requiring minimal signal-chain re-architecture. The A1 gives the best noise performance but its 15 dB gain may be too high, potentially overdriving the ADC — though the gain can be trimmed slightly downward with external input resistors. The C1 at only 5 dB gain is likely too low to be a direct LMH5401 replacement. All three share the same 12-pin WQFN package (not pin-compatible with the LMH5401's 14-pin UQFN), so a board redesign is needed regardless of variant.  For the best balance of noise improvement and gain fit to your existing LMH5401 design, the TRF1305B1 is likely the easiest drop-in from a system perspective, while the TRF1305A1 is the best choice if lowest noise floor is the priority and you can accommodate the higher gain.

Regards,
Hruday