the clock signal the switch 30 causes the common pole 36 to be repeatedly coupled to the first pole 32 then decoupled from the first pole 32 and coupled to the second pole 34 then decoupled from the second pole 34 and coupled back to the first pole 32 and so on the common pole 36 is never coupled to both the first and second poles 32 34 simultaneously as a result a charge is transferred between the charge supply 40 and the charge transfer capacitor 42 whenever the common pole 36 is coupled to the second pole 34 similarly the charge is transferred between the coupling capacitor 14 and the charge transfer capacitor 42 whenever the common pole 36 is coupled to the first pole 32 the rate at which the charge is transferred is proportional to the frequency of the clock signal which is an oscillating voltage signal thus by controlling the frequency of the clock signal the rate of discharge of the coupling capacitor 14 can be controlled for example in the event the proximal electrode 15 of the coupling capacitor 14 carries a negative charge after a stimulation pulse from the therapy circuit 18 passes through the coupling capacitor 14 as is typically the case the charge supply 40 is selected to supply positive charge.