The bias current sources

The various bias currents of the analog stages described in section 1 are generated by 8 bit digital to analog converters which are controlled by registers of the same name. The conversion slope of the DACs is $2.5 \mu$A/LSB with a register value of 0 corresponding to zero output current. To achieve correct operation of the bias generator circuit, a reference current of $100\mu\/$A must be flowing into the IrefIn pad which can be generated either by an external source or by using the internal reference current generator. When using the latter, IrefOut has to be bonded directly to IrefIn and a resistor of $20 k \Omega$ must be connected from Rref to Vssa (-2V). For good blocking of the reference current, it is recommended to have 100nF parallel to the resistor.