Voltage output R-2R DACs eliminate the need for an external amplifier for many users. Depending on the digital input code, switches will connect the resistors to either the reference voltage or the ground level to realize a programmable voltage divider. However, the reference load impedance will vary with code, and is thus harder to drive quickly and accurately. Reference source impedance will degrade linearity and dynamic performance. The output impedance does not vary with DAC code, so these can be used unbuffered in many applications (see LTC2641). For buffered DACs, the user must be willing to live with the performance compromise of the internal buffer amplifier. Users requiring wider output range, large load capacitance, or high drive current often add an external amplifier anyway. Note that this amplifier sees large swings at the input, so large-signal common-mode rejection and the stability of offset voltage and input bias current over the full rail-to-rail input range can degrade the INL.