A telemetry receive unit for use in an implantable medical device or system can include a coil unit, a single-bit analog to digital converter (ADC), a finite impulse response filter (FIR) coupled to the single-bit ADC, and an accumulator coupled to one or more filter taps of the FIR filter. The accumulator, in operation, can produce one or more data recognition signals corresponding to sampled bits at least temporarily stored at the FIR filter. In several examples, the data recognition signals discriminate between frequency modulated signals that are received at the coil unit, including frequency shift keying (FSK) modulated signals.