V_OS affects the signal conditioning ability of an op amp circuit in both AC-coupled and DC-coupled circuits. Figure 6-2 shows an AC-coupled inverting op amp. The capacitor C₁ AC-couples the input from the previous stage, and C₂ AC-couples the output to the load. Thus, C₁ prevents any DC current from flowing through R_F and R_G (with the exception of bias currents) and C₂ prevents any DC current from flowing into the load. V_OS appears across the inputs. Because there is no DC current flow, the amplifier is in unity gain and the output is at the same potential as the inverting input. This is the case even if the output is not DC-coupled (C₂ is not present), because V_OS does not appear across R_G. The capacitors also serve to establish some filtering in the circuit.

Figure 6-2 AC-Coupled Inverting Amplifier

When C₁ is removed from the circuit, the amplifier is DC-coupled to the signal source. This is the case with many transducers, such as temperature sensors and strain gauges, and DACs. Transducers output voltages, currents, or resistances, and the latter two outputs require conversion to voltage. Such applications require DC conversions, where V_OS and the drift play a big part in the accuracy. With C₁ removed, the V_OS of the op amp is multiplied by the non-inverting gain (1+R_F/R_G) of the circuit, and is added to any DC offset of the source multiplied by the signal gain (–R_F/R_G). The worst case is when the two offsets add together. If the gain of the circuit is large, either the dynamic range is greatly reduced or the output is saturated. If C₂ is also removed, the load now has a DC-offset applied, worsening the situation.

Audio power amplifiers use AC-coupling at the input to prevent any DC-voltage component of the input signal from adding to the DC level of the audio circuit (which is normally set to the mid-rail of the power supply for maximum dynamic range). For single-ended loads such as headphones, the output is AC-coupled to prevent any DC voltage from being dropped across the speakers, which might possibly damage the speakers.

V_OS also reduces the dynamic range of an ADC. The loss of dynamic range affects the resolution of ADC circuits because maximum dynamic range is required for maximum resolution. Table 6-2 shows the resolution of a least significant bit (LSB) for various input voltage ranges. Usually, an op amp can be chosen with a low enough V_OS to meet the desired resolution. It is easy to find an op amp that meets the V_OS specification for an 8- or 10-bit converter, but becomes increasingly difficult as the resolution increases. High-speed, low-voltage acquisition circuits can require AC-coupling at the op amp input to remove offset contribution from previous stages. An alternative is AC-coupling the op amp output prior to the ADC input to remove the DC component, particularly if the V_OS is higher than desired (see Op Amps for Everyone). This is especially true of the high-speed op amps, which often have a high V_OS. The number of bits of error introduced by a given V_OS is given by the number of bits, equal to A_CLV_IO/LSB, where A_CL is the closed-loop gain and LSB is V_(fullscale)/2^N is the least significant bit of the ADC.

High-speed amplifier circuits often use AC-coupling of the inputs and outputs to minimize the magnitude of V_OS, particularly in circuits that have a high gain. When AC-coupling is not possible or is not feasible for some reason, then DC feedback or op amps with calibration can be employed to reduce V_OS.