Patent ID: 7012969

Claim:
A distortion compensating apparatus having a memory for storing distortion compensation coefficients, which are for compensating for distortion of a transmission power amplifier, in association with power p of a transmit signal x(t), a predistortion unit for reading a distortion compensation coefficient h n (p) where n means a current value, which conforms to power p of the transmit signal x(t), out of said memory and subjecting the transmit signal x(t) to a distortion compensation processing using the distortion compensation coefficient h n (p), a digital-to-analog (DA) converter for converting a digital transmit signal, which has been subjected to the distortion compensation processing, to an analog signal, a distortion compensation coefficient calculation unit for calculating a distortion compensation coefficient h n+1 (p) based upon the transmit signal x(t) before the distortion compensation thereof and an output signal of the transmission power amplifier where n+1 means a newly calculated value, and a distortion compensation coefficient h n (p) updating unit for updating the distortion compensation coefficient by storing the calculated distortion compensation coefficient h n+1 (p) in said memory in association with the power of the transmit signal x(t), said apparatus comprising: a comparator for comparing power Pa of the transmit signal x(t), compensated with the calculated distortion compensation coefficient h n+1 (p), and an upper-limit power Pmax before the calculated distortion compensation coefficient h n+1 (p) calculated by said distortion compensation coefficient calculation unit is stored in said memory; and a distortion compensation coefficient correction unit for correcting the calculated distortion compensation coefficient h n+1 (p) in such a manner that power Pa of the transmit signal x(t) will fall below the upper-limit power Pmax; wherein said distortion compensation coefficient updating unit updates the distortion compensation coefficient h n (p) by storing a corrected distortion compensation coefficient h n+1 (p)′ in said memory when the power Pa of the transmit signal x(t) is greater than the upper-limit power Pmax and storing the calculated distortion compensation coefficient h n+1 (p) in said memory when the power Pa is less than the upper-limit power Pmax.