PLs. introduce a method of conversion from one single-end BB signal to 4 IQ signals

Hello,all,

I want to use a RF modulator which needs four IQ signals(TxBBIN/TxBBIP/TxBBQN/TxBBQP),and I know these BB signals are generally produced by DSP or ARM circuit.
My question is that I have only one BB signal from MCU, how can I deal with it and transfer it to four IQ signals? thanks a lot!