Transmitter predistortion circuit and method therefor

A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:

• processing a forward-data stream to produce a processed-forward-data stream;
• converting said processed-forward-data stream into a forward-analog signal using a digital-to-analog converter (D/A);
• propagating said forward-analog signal through said analog-transmitter components to generate a return-analog signal;
• converting said return-analog signal into a return-raw-digitized-data stream using an analog-to-digital converter (A/D);
• compensating, in response to said forward-data stream, for quantization errors introduced into said return-raw-digitized-data stream by said A/D to produce a return-data stream;
• and
• altering said processed forward-data stream in response to said return-data stream;
• wherein said A/D includes a quantizer;
• and
• said compensating activity comprises evaluating said quantizer, programming a quantizer-simulator in response to said evaluating activity, operating said guantizer-simulator in response to said forward-data stream to generate a quantize-simulated-data stream and determining a difference between said forward-data stream and said quantize-simulated-data stream

A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:

• processing a forward-data stream to produce a processed-forward-data stream;
• converting said processed-forward-data stream into a forward-analog signal using a digital-to-analog converter (D/A);
• propagating said forward-analog signal through said analog-transmitter components to generate a return-analog signal;
• converting said return-analog signal into a return-raw-digitized-data stream using an analog-to-digital converter (A/D);
• compensating, in response to said forward-data stream, for errors introduced into said return-raw-digitized-data stream by said A/D to produce a return-data stream;
• and
• altering said processed forward-data stream in response to said return-data stream;
• wherein said forward-data stream is configured to convey a plurality of frequency-multiplexed communication channels;
• and
• said altering activity is configured so that distortion introduced by said analog-transmitter components is reduced, and said distortion is reduced in a way that achieves greater reduction in error-vector magnitude (EVM) for ones of said communication channels having higher EVM's than is achieved for communication channels having lower EVM's.

A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:

• an equalizer configured to receive a forward-data stream that conveys a plurality of frequency-multiplexed communication channels and to generate a processed-forward-data stream which propagates toward said analog-transmitter components;
• an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components;
• a first signal-strength-measuring circuit adapted to receive said forward-data stream and configured to identify a communication-signal strength for each of said communication channels;
• a second signal-strength-measuring circuit coupled to said A/D and configured to identify an error-signal strength for each of said communication channels;
• and
• a control circuit coupled to said first and second signal-strength-measuring circuits and to said equalizer, said control circuit being configured to adapt coefficients of said equalizer in response to relative communication-signal strengths and error-signal strengths for said communication channels to counteract distortion introduced by said analog-transmitter components.

A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:

• an equalizer configured to receive a forward-data stream and to generate a processed-forward-data stream;
• a digital-to-analog converter (D/A) coupled to said equalizer and configured to convert said processed-forward-data stream into a forward-analog signal which propagates through said analog-transmitter components;
• an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components, said return-analog signal being responsive to said forward-analog signal, and said A/D being configured to produce a return-raw-digitized-data stream;
• an A/D compensation section adapted to receive said forward-data stream, said A/D compensation section being configured to compensate for quantization errors introduced into said return-raw-digitized-data stream by said A/D and to produce a return-data stream;
• and
• a control circuit coupled to said equalizer, said control circuit being configured to alter said processed-forward-data stream in response to said return-data stream
• wherein said A/D includes a quantizer characterized by switching thresholds;
• and
• said A/D compensation section comprises a quantizer-simulator configured to simulate said guantizer when programmed with said switching thresholds which characterize said quantizer, said quantizer-simulator being adapted to receive said forward-data stream and to generate a quantize-simulated-data stream, and a differencing circuit configured to determine a difference between said forward-data stream and said quantize-simulated-data stream.

A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:

• an equalizer configured to receive a forward-data stream and to generate a processed-forward-data stream;
• a digital-to-analog converter (D/A) coupled to said equalizer and configured to convert said processed-forward-data stream into a forward-analog signal which propagates through said analog-transmitter components;
• an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components, said return-analog signal being responsive to said forward-analog signal, and said A/D being configured to produce a return-raw- digitized-data stream;
• an A/D compensation section adapted to receive said forward-data stream, said A/D compensation section being configured to compensate for errors introduced into said return-raw-digitized-data stream by said A/D and to produce a return-data stream;
• and
• a control circuit coupled to said equalizer, said control circuit being configured to alter said processed-forward-data stream in response to said return-data stream;
• wherein said forward-data stream is configured to convey a plurality of frequency-multiplexed communication channels;
• and
• said control circuit is configured so that distortion introduced by said analog-transmitter components is reduced, and said distortion is reduced in a way that achieves greater reduction in error-vector magnitude (EVM) for ones of said communication channels having higher EVM's than is achieved for communication channels having lower EVM's.