  In this work, we design and implement frequency-robust Molmer-Sorensen gates
on a linear chain of trapped ions, using Gaussian amplitude modulation and a
constant laser frequency. We select this frequency to balance the entanglement
accumulation of all motional modes during the gate to produce a strong
robustness to frequency error, even for long ion chains. We demonstrate this
technique on a three-ion chain, achieving $<\,1\%$ reduction from peak fidelity
over a $20\,$kHz range of frequency offset, and we analyze the performance of
this gate design through numerical simulations on chains of two to 33 ions.
