RECONSTRUCTION FILTER

LOW COST

This analogue reconstruction filter has been designed to be used in conjunction with a Half–Band Interpolating / Decimating Digital filter such as the TRW TMC2242 or with devices employing an output D-A which incorporates digital filters such as the TRW digital video encoder TMC22190.

With the increasing use of High quality video techniques in applications outside the professional broadcast field such as Multimedia, engineers are looking to include a degree of filtering in the A-D and D-A processing while avoiding the use of large and expensive filters.



When such digital filters are used with double speed oversampling video A-D and D-A converters they simplify the type of analogue antialiasing pre filters and reconstruction post filter required.

It is seen from manufacturers information that this type of digital filter has very good attenuation between the frequencies of Fs/4 and 3Fs/4 where Fs is the PXCK (Master Clock) rate. When the normal PXCK rate of 27MHz is used the signal can be expected to have very little energy between 6.75MHz and 20.25MHz.

In order to preserve the integrity of the signal any analogue filter used must have a passband response similar to the requirements of CCIR 601 but, due to the considerations above, it is not required to have significant attenuation below 21MHz.

These considerations allow a filter to be designed which has good amplitude and group delay response to 5.75MHz, good attenuation at 21MHz, small size and low cost.

THE FARADAY FL453 AND FL454 MEET THESE CRITERIA.

As additional features a zero has been placed at 27MHz to maximise the suppression at the PXCK rate and sinx/x correction may be added by simply grounding one pin in the device. Through hole and surface mount versions are available.