Digital predistortion transmitter
There is a need for effectively compensating distortion when a predistortion transmitter is subject to not only a memory effect due to nonlinearity of an amplifier, but also a modulator's DC offset, IQ unbalance, or local quadrature error. A predistortor to be used is a polynomial predistortor including a polynomial basis generation portion and an inner product calculation portion. The polynomial basis generation portion delays a real part and an imaginary part of a complex input signal Sx=Ix+jQx for up to M samples to generate 2(M+1) signals, duplicately combines these signals to generate monomials having maximum degree N, and outputs, as a basis vector, all or part of the monomials depending or needs. The inner product calculation portion performs an inner product calculation using a coefficient vector, i.e., a set of complex numbers sized equally to the basis vector to find a polynomial value and outputs the value as a complex signal.
1. A transmitter comprising:
a DA converter which converts complex signal into analog signal;
a power amplifier which amplifies the analog signal to be outputted and outputs an output signal with the amplified analog signal;
an AD converter which coverts the output signal into an outputted complex signal;
a coefficient vector generator which generates a coefficient vector on the basis of the outputted complex signal and a first input complex signal inputted from an external of the transmitter;
a digital predistortor includes
a signal vector generator which generates a signal vector on the basis of the first complex input signal and a second complex input signal which has been inputted before the first input complex signal;
a complex signal generator which generates the complex signal to be converted by the DA converter on the basis of the coefficient vector and the signal vector.
2. A transmitter according to claim 1 ,
further comprises a memory which holds the second complex input signal wherein the signal vector generator obtains the second complex input signal from the memory for generating a signal vector.
3. A transmitter according to claim 1 ,
wherein the coefficient vector generator which generates a residual signal on the basis of difference between the first complex input signal and the outputted complex signal.