The note on page 13 -14 of the HMC981LP3E data sheet reads "Please note that the external negative voltage should be between -2.5V to -3.5V for HMC981LP3E to operate. If your application requires negative voltages outside this range please contact Hittite application support". The amplifier that I'm using can not go below -1.5 volt for normal operation and -2.0 volts for the absolute max. What are your recommendations / suggestions? Thanks.