3 Bandwidth

Typical voltage feedback op amps have a low frequency pole present in their AC response, limiting the bandwidth of the device. The frequency response is similar to that of a low pass filter, with reduced gain at higher and higher frequencies. The bandwidth of the amplifier circuit is determined by dividing the gain bandwidth product (GBW) of the op amp by the closed-loop gain of the amplifier circuit. The GBW is specified in the op amp’s datasheet Electrical Characteristics table.

For example, the GBW of the OPA2210, a precision op amp, is 18MHz. For an application requiring a high gain of 1000 V/V (60dB), the effective bandwidth of a single-stage amplifier is a mere 18kHz (AC response of this circuit is shown in Figure 4-2). While this may be plenty for a near-DC application, there are many applications that demand both high gain and high bandwidth. A high speed op amp with a higher GBW product can be used to extend the bandwidth of the system at high gains, but typically it will come at the expense of DC precision.

Few devices in the marketplace can satisfy the needs of high DC precision, gain and bandwidth in a single amplifier stage. Instead, multiple precision op amps can be cascaded to preserve bandwidth while maintaining low offset and low noise for high gain applications.