Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H17/00—Networks using digital techniques
  • H03H17/02—Frequency selective networks
  • H03H17/0248—Filters characterised by a particular frequency response or filtering method
  • H03H17/0264—Filter sets with mutual related characteristics
  • H03H17/0273—Polyphase filters
  • H03H17/0275—Polyphase filters comprising non-recursive filters
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H17/00—Networks using digital techniques
  • H03H17/02—Frequency selective networks
  • H03H17/0294—Variable filters; Programmable filters
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H17/00—Networks using digital techniques
  • H03H17/02—Frequency selective networks
  • H03H17/06—Non-recursive filters
  • H03H17/0621—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
  • H03H17/0635—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies
  • H03H17/065—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies the ratio being integer
  • H03H17/0657—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies the ratio being integer where the output-delivery frequency is higher than the input sampling frequency, i.e. interpolation
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H17/00—Networks using digital techniques
  • H03H17/02—Frequency selective networks
  • H03H17/06—Non-recursive filters
  • H03H17/0621—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
  • H03H17/0635—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies
  • H03H17/065—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies the ratio being integer
  • H03H17/0664—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies the ratio being integer where the output-delivery frequency is lower than the input sampling frequency, i.e. decimation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/14—Picture signal circuitry for video frequency region
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
  • H04N5/445—Receiver circuitry for the reception of television signals according to analogue transmission standards for displaying additional information
  • H04N5/45—Picture in picture, e.g. displaying simultaneously another television channel in a region of the screen

Definitions

• the invention relates to a filter device for changing a sample rate of a discrete representation, e.g. to change a size of an image signal, and to an image display apparatus comprising such a filter device.
• a first aspect of the invention provides a filter device as defined in claim 1.
• a second aspect of the invention provides an image display apparatus comprising such a filter device.
• a filter device for changing a sample rate of a discrete representation, e.g. to change a size of an image signal comprises a plurality of multipliers, summing circuitry coupled to outputs of the multipliers, and a plurality of delay cells arranged for repeatedly supplying identical values to corresponding ones of the multipliers during a number of times corresponding to an expansion ratio by which the discrete representation is to be expanded, or for, in cooperation with the summing circuitry, accumulating output values from the multipliers during a number of times corresponding to a compression ratio by which the discrete representation is to be compressed.
• expansion is synonymous to up-sampling
• compression is synonymous to down-sampling.
• the sample rate conversion filter device of the present invention is elucidated by means of the example of an image size changer, other discrete representations like digital or time-discrete sound, and designs of character fonts, textiles or wallpaper patterns are by no means excluded.
• the filter device in accordance with the present invention, no input samples are skipped in the case of a compression, as the circuit processes all input samples which are presented. Reversely, in the case of an expansion, the delay cells repeatedly furnish samples to the multipliers, thereby generating the basis for obtaining additional output samples.
• the invention encompasses filter devices which are only suitable for compression, filter devices which are only suitable for expansion, as well as reconfigurable filter devices which are suitable for both compression and expansion.
• Fig. 1 shows an embodiment of an expansion filter in accordance with the present invention
• Fig. 2 shows an embodiment of a compression filter in accordance with the present invention
• Fig. 3 shows an embodiment of an image display device comprising a filter device in accordance with the present invention which is suitable for both compression and expansion.
• Fig. 1 shows an embodiment of an expansion filter in accordance with the present invention and illustrates how the normal (polyphase) FIR filter structure is modified to allow for expansion. In case of expansion, there are more output samples than there are input samples.
• an input signal I is applied to a first delay unit (SO, DO) which comprises a switch SO and a delay cell DO.
• the switch SO applies either the input signal I or an output signal of the delay cell DO, to the delay cell DO.
• the switch SO is controlled by a hold signal H.
• the delay cell DO imposes a delay of one sampling period Ts.
• a delay cell with a write-enable input receiving the hold signal H would do.
• a cascade connection of delay units (SI, DI), (S2, D2), and (S3, D3), each having a similar construction as the delay unit (SO, DO), is connected to the output of the delay cell DO.
• Multipliers MO, Ml, M2, and M3 multiply the output signals of the delay cells DO, DI, D2, and D3, respectively, by (variable) coefficients CO, Cl, C2, and C3, respectively. With variable coefficients C0-C3, a polyphase filter is obtained.
• Adders Al, A2, and A3 sum the outputs of the multipliers MO, Ml, M2, and M3, to furnish an output signal O.
• the hold signal puts the switches Si in the state shown during a first sampling period, and then in the state not shown for the following three successive sampling periods.
• each input sample is supplied four times by the delay cells Di.
• the filter device is a polyphase filter, in which the coefficients Ci are different for each sampling period Ts.
• Fig. 2 shows an embodiment of a compression filter in accordance with the present invention.
• compression there are (far) fewer output samples than there are input samples. This is downsampling or decimation.
• the bandwidth of the interpolation filter must be reduced to fit the lowest of the two sample rates, in this case the output sample rate.
• the filter is constant, i.e. it is related to the input side (where the sample rate is constant).
• Compression or downsampling means losing samples, thus losing information, and thus aliasing.
• a conventional FIR filter interpolator a low-pass pre- filter (“anti-aliasing filter") is required to fulfil the sampling theorem requirement.
• the pre-filter bandwidth must be decreased. This makes it very awkward to apply the conventional FIR filter interpolator implementation for variable compression like e.g. geometry correction.
• a variable compression rate requires a variable pre-filter. Another solution is needed.
• Fig. 2 illustrates how the inverted FIR filter structure must be modified to allow for good compression.
• an input signal I' is applied to multipliers M3', M2', Ml', and MO' for multiplication by respective factors C3', C2', Cl', and CO'.
• Outputs of the multipliers M3 ⁇ Ml', and MO' are coupled to accumulator units (S3', A3', D3'), (SI', Al', DI'), and (SO', A0', DO').
• Each accumulator unit (Si', Ai', Di') comprises a switch Si', an adder Ai', and a delay cell Di'.
• the switch Si' applies either an output signal of the previous accumulator unit (for switch S3': a zero value) or an output signal of the delay cell Di', to the adder Ai'.
• the adder Ai' adds the signal received from the switch Si' to the output of the multiplier Mi', and applies the sum to the delay cell Di'.
• the last delay cell DO' furnishes the output signal O' of the filter device of Fig. 2.
• the switches Si' are controlled by a hold signal H'. For a compression ratio of e.g. 4: 1, the hold signal H' keeps the switches Si' in the state shown for one sample period Ts, and in the state not shown for the following three successive sampling periods. Sometimes, only the fractional part of the delay changes.
• the delay cells Di' do not shift, only the coefficients Ci of the filter are changed.
• a new input sample will be used to calculate its contribution to the same output sample data set (same integer delay). This output is accumulated with the other contents of the delay cells. Only when the integer part of the delay (or destination address) changes, then the storage elements shift the data out (one at a time).
• the calculation rate must be coupled to the side (input or output) with the highest sample rate (for compression: the input) and the filter bandwidth must be coupled to the side with the lowest sample rate (for compression: the output). This is the exact purpose of the reversal of input and output. Very high compression rates can be achieved without pre-filtering.
• Fig. 3 shows an embodiment of an image display device comprising a filter device in accordance with the present invention which is suitable for both compression and expansion.
• Fig. 3 is a combination of Figs. 1 and 2, suitable for both compression and expansion.
• the input signal I is applied to a cascade connection of delay units (SO, DO) .. (S5, D5) as in Fig. 1.
• Outputs of the delay cells Di are applied to multipliers MO .. M5 thru selectors SEL-0 .. SEL-5.
• the multipliers Mi multiply by variable coefficients CO .. C5 selected from coefficient arrays or obtained from a function generator (not shown); there are preferably 64 different coefficients in each array, which coefficients are selected by means of a phase signal Ph.
• Outputs of the multipliers MO .. M5 are summed by adders Al .. A5 to obtain a result which is applied to a first input of an output selector SEL-out.
• the input signal I is also applied to second inputs of the selectors SEL-0 .. SEL-5 thru a sealer SC.
• the outputs of the multipliers Mi are also applied to accumulation units (Si', Ai', Di') as in Fig. 2.
• the output of the delay cell DO' is applied to a second input of the output selector SEL-out.
• the selectors SEL-i pass the outputs of the delay cells Di to the multipliers Mi, as in Fig. 1, and the output selector SEL- out selects its first input signal, i.e. the output of the adder A5.
• the selectors SEL-i pass the output of the sealer SC directly to the multipliers Mi, as in Fig. 2, and the output selector SEL-out selects its second input signal, i.e. the output of the delay cell DO'.
• the filter device of Fig. 3 further comprises a control, initialization and mode select unit CTRL which determines a mode signal (compression / expansion) M and filter coefficients Fc on the basis of received input parameters IP.
• a calculation unit CALC determines a zoom factor, the coefficient phase signal Ph, and the hold signal H which determines the states of the switches Si, Si', from data received from the control unit CTRL.
• the calculation unit CALC also controls a clip and round circuit which furnishes the output signal of the filter device on the basis of the output signal of the output selector SEL-out.
• the output signal O is displayed on a display unit DU.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• Mathematical Physics (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Image Processing (AREA)
• Television Systems (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

Family

ID=8224535

Family Applications (1)

Country Status (6)

Cited By (4)

Families Citing this family (19)

Family Cites Families (5)

• 1997
  • 1997-09-26 DE DE69708841T patent/DE69708841T2/de not_active Expired - Lifetime
  • 1997-09-26 EP EP97940285A patent/EP0870364B1/en not_active Expired - Lifetime
  • 1997-09-26 JP JP52022098A patent/JP4356819B2/ja not_active Expired - Fee Related
  • 1997-09-26 WO PCT/IB1997/001166 patent/WO1998019396A2/en not_active Ceased
  • 1997-09-26 KR KR10-1998-0705128A patent/KR100475201B1/ko not_active Expired - Fee Related
  • 1997-10-28 US US08/959,348 patent/US5892695A/en not_active Expired - Fee Related

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