Arrangement for compensating errors in a quadrature modulator

Claim 1

An arrangement for compensating errors occurrent in a quadrature modulator which includes means (1) for generating two quadrature signals in the baseband, cos a(t) and sin a(t), to a first and a second branch respectively in the modulator; means (2) for generating two high frequency signals (cos wt, sin wt) with a mutual phase difference of 90 degrees; mixers (3,4) for mixing the quadrature signals, with the high frequency signals (cos wt, sin wt) and an adder (5) for producing the sum of the output signals of said mixers (3,4), characterized in that the arrangement further includes adjustable signal generating means (14, 16, 21) for generating a first (k1), a second (k2) and a third (k3) signal; a means (11) incorporated in said first branch of the modulator for forming a fourth signal which constitutes the product of the cos a(t) quadrature signal and said first signal (k1); a means (17) for forming a fifth signal which constitutes the product of the sin a(t) quadrature signal and said second signal (k2); a means (12) incorporated in said first branch for forming a sixth signal which constitutes the difference between said fourth signal and said fifth signal; and a means (19) incorporated in said second branch of the modulator for forming a seventh signal which constitutes the product of the sin a(t) quadrature signal and said third signal (k3), whereby amplitude error and phase error are compensated by suitably adjusted values of said first to third signals (k1-k3).