Quantizer for a DPCM encoder
AssigneeSiemens Aktiengesellschaft
InventorHans-Joachim Grallert
Life of this patent
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Abstract
A difference pulse code modulation ("DPCM") encoder for encoding and compressing digital data. This encoder includes a quantizer formed by a read-only memory (ROM). DPCM signal values to be quantized are supplied without a sign bit as addresses to the ROM; the code words read-out as data from the ROM in response to addresses represent the quantized DPCM signal values. The size of the ROM required for this purpose is reduced by limiting the DPCM signal values which are supplied as addresses to the ROM. The sign bit contained in the DPCM signal values is not supplied to the ROM but is added to the code words read-out of the ROM as quantized DPCM signal values. In addition, the DPCM signal values and also the code words read out of the ROM are rounded off by omission of the least significant bit.
Claims10
A digital data quantizer for a difference pulse code modulation ("DPCM") encoder comprising, in combination:
- (a) quantizer input means for receiving DPCM signals having numerical value ("NV") bits and a sign bit;
- (b) limiter means, connected to receive said NV bits from said quantizer input means, for producing a first digital output signal of constant value when the numerical value of the NV bits received exceeds an upper limit, and second digital output signals of variable value when the numerical value of the NV bits received falls below said upper limit, the values of said second output signals being dependent upon said numerical values;
- (c) read-only memory means having an address input and a data output, said address input being connected to receive the output signals of said limiter means for producing, at said data output, quantized DPCM digital signal values in response to the receipt of said output signals;
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- (d) quantizer output means, connected to said data output of said read-only memory means for receiving said quantized DPCM signal values, and connected to said quantizer input means for receiving said sign bit.
Dependencies are inferred from the claim text.