An arrangement for saving energy in a radio device transmitter and a radio device.
The steady currents of the transmitter amplifiers are made dependent on the transmitting
power for reducing the losses of the amplifiers. The VGA (400) comprises
at least one main differential pair (Q41-Q42; Q43-Q44)
for controlling the gain and a bias differential pair (Q47-Q48) for
controlling said steady currents. These pairs are steered by the one and the same
voltage (V), in which case the output current (Ib1; Ib2)
of the bias differential pair changes in the same way as the output current (io1;
io2) of the main differential pair when the gain is readjusted. The
output current of the bias differential pair is used as a bias current of the transmitter
amplifiers, i.e. as a current that determines the steady currents of the amplifiers.
Because the values of the steady currents of the amplifiers track accurately the
value of the gain, when this is changed, the steady currents are always so low
as the transmitting power necessarily requires, at a given time, wherein the amount
of needless losses, from the transmitting operation's point of view, is small.
Said differential pairs are placed on one and the same substrate, in order to the
control to function accurately in a wide dynamic range.
