We present characterization of a lock-in amplifier based on a field
programmable gate array capable of demodulation at up to 50 MHz. The system
exhibits 90 nV/sqrt(Hz) of input noise at an optimum demodulation frequency of
500 kHz.The passband has a full-width half-maximum of 2.6 kHz for modulation
frequencies above 100 kHz. Our code is opensource and operates on a
commercially available platform