Posted on: July 1, 2014

What is Bandwidth?

The width measurement of a frequency range, measured in hertz, of a function or a frequency variable. The bandwidth specifies the difference between the upper and lower frequencies of an ac source in which the signal is at least 70 percent of full scale power. The bandwidth is a central concept in various electronics and telecommunication fields.

The two common power supply designs have varying bandwidth responses. Linear power supplies have higher bandwidths response but are less efficient as compared to the switched mode power supply units.

The SMPSs have improved characteristics as compared to the linear supplies and can operate at higher frequencies. This allows them to have better efficiency, low power losses and small sized components. However, they have narrower bandwidth and require external bandwidth control components unlike in the linear units.

Components and filter circuits

The bandwidth of components used in electronic circuits is critical in the design stage. Components such as transistors, integrated circuits and capacitors should have bandwidths which are wider than the circuit operation bandwidth.

Filter circuits made of capacitors, inductors and resistors are used to shape the bandwidth of a circuit. Different configurations are used based on required frequency range. The filter is configured such that it only allows the desired range of frequencies to pass, while blocking all frequencies falling outside the desired bandwidth.

Bandwidth in power supply units

A power supply unit with a wide bandwidth is preferred; the switched mode power supply which can be driven at high frequencies provides this opportunity. The programmable switched mode supplies using remote bandwidth control circuits offers a wide range of voltages over a wide bandwidth which can still be extended beyond the design bandwidth.

A switched mode power supply uses a feedback loop utilizing either current or voltage feedback, and which allows one to control the bandwidth and output impendence of the supply. By controlling the bandwidth and the impendence, a legacy power unit can be emulated in an automatic test system.

The high switching frequency in SMPS means small sized output inductor and capacitor filter components hence a cost reduction. And the associated high bandwidth improves the load transient response. However, the higher switching frequencies lead to higher AC-related losses which may necessitate the need for larger heat sink and board space to dissipate the heat.

A wide bandwidth supply is able to recover from large load currently quickly; however, its output stages may be affected by the loads circuit impendence more than a narrowband supply. The high reactance of a load may influence the control loop behavior by either increasing or decreasing the bandwidth and hence changing the transient response as well as the ripple rejection ability of the supply.