COMPARISON BETWEEN DIGITAL AND ANALOG FILTERS?

BASE OF DIGITAL AND ANALOG FILTERS DESIGNING
Normally resistors,inductors and capacitors are called analog components and are used to design analog filters,but on the other hand differential equations are used for the implementation of digital filters.

analog filter

       

digital filter

BASIC TYPES OF FILTERS


a) FIR FILTERS

b) IIR FILTERS

COMPARISON BETWEEN ANALOG AND DIGITAL FILTERS

DIGITAL FILTERS                                                                         ANALOG FILTERS
one digital filter can filter many input signals                              this is not possible in analog filters
digital filters have linear phase                                                     analog filters do not have linear phase
environmental factors have no effect                                            it depends upon environmental factor
for further use filtered and unfiltered data can be saved               but here data saving is not possible
digital filter is portable                                                                  analog filter is not portable
digital filters are flexible filters                                                     analog filters are not flexible filters
VLSI technology can reduce hardware of digital filter                 hardware reduction is difficult
power consumption can be controlled                                          control of power consumption is hard
digital filters can work with low frequencies                                they operate at high frequencies
maintenance is not required                                                           maintenance is required
their speed is low                                                                           speed is high
digital filter bandwidth is very small                                            bandwidth is extremely large
accuracy is less                                                                              high accuracy
digital filter is effected by ADC noise                                          not affected by ADC noise
digital filter is affected by round off noise                                   not affected by this noise
development and design time is more                                          design time is less
digital filter is described by difference equation                         differential equation explains this filter
T.F. H(z) should be rational for stability &causality                   T.F.H(s) should be rational here too.
filter coefficients are used for required response                         approximation techniques are used
it works on digital samples of signals                                          it works on analog samples of dignal
adders,subtractors,delays are used for implementation               resistors,capacitors,inductors are used
here poles should lie inside unit circle in z-plane                       poles should lie on left half of s-plane

Comparison of analog and digital filters Descriptive

Digital filters are not subject to the component non-linearities that greatly complicate the design of analog filters. Analog filters consist of imperfect electronic components, whose values are specified to a limit tolerance (e.g. resistor values often have a tolerance of ±5%) and which may also change with temperature and drift with time. As the order of an analog filter increases, and thus its component count, the effect of variable component errors is greatly magnified. In digital filters, the coefficient values are stored in computer memory, making them far more stable and predictable.[9]

Because the coefficients of digital filters are definite, they can be used to achieve much more complex and selective designs – specifically with digital filters, one can achieve a lower passband ripple, faster transition, and higher stopband attenuation than is practical with analog filters. Even if the design could be achieved using analog filters, the engineering cost of designing an equivalent digital filter would likely be much lower. Furthermore, one can readily modify the coefficients of a digital filter to make an adaptive filter or a user-controllable parametric filter. While these techniques are possible in an analog filter, they are again considerably more difficult.

Digital filters can be used in the design of finite impulse response filters. Analog filters do not have the same capability, because finite impulse response filters require delay elements.

Digital filters rely less on analog circuitry, potentially allowing for a better signal-to-noise ratio. A digital filter will introduce noise to a signal during analog low pass filtering, analog to digital conversion, digital to analog conversion and may introduce digital noise due to quantization. With analog filters, every component is a source of thermal noise (such as Johnson noise), so as the filter complexity grows, so does the noise.

However, digital filters do introduce a higher fundamental latency to the system. In an analog filter, latency is often negligible; strictly speaking it is the time for an electrical signal to propagate through the filter circuit. In digital systems, latency is introduced by delay elements in the digital signal path, and by analog-to-digital and digital-to-analog converters that enable the system to process analog signals.

In very simple cases, it is more cost effective to use an analog filter. Introducing a digital filter requires considerable overhead circuitry, as previously discussed, including two low pass analog filters.

Another argument for analog filters is low power consumption. Analog filters require substantially less power and are therefore the only solution when power requirements are tight.

When making an electrical circuit on a PCB it is generally easier to use a digital solution, because the processing units are highly optimized over the years. Making the same circuit with analog components would take up a lot more space when using discrete components. Two alternatives are FPAA's[10] and ASIC's, but they are expensive for low quantities.Courtesy of wikipedia...