DETAILED DESCRIPTION OF THE INVENTION Referring to FIG.
3 there is shown a block diagram of a third phaseshifter configuration for use with an IQ modulator.
In this configuration, .
+-.
45.
degree.
phaseshifters P1 and P2 are moved to the outputs of M1 and M2, respectively, and LO directly drives M1 and M2.
Advantages of this configuration include the following.
First, the LO power can be reduced over the circuits of FIGS.
1 and 2, in that LO is required to drive only M1 and M2, and not P1 and P2, or P1'.
Second, in that P1 and P2 are positioned at the outputs of M1 and M2, respectively, P1 and P2 do not experience the non-linear loading effect that is found at the inputs to the mixers.
It should be noted, however, that care must be taken to ensure that P1 and P2 not only phaseshift their respective input signals by 45.
degree.
, but that they also delay their respective signals by the same amount of time.
The latter requirement becomes more difficult to realize if the output bandwidth is wide compared to the center frequency.
FIGS.
4 and 5 are each a schematic diagram illustrating a first and a second embodiment of the invention, respectively.
FIGS.
4 and 5 are specific, preferred implementations of the circuit configuration shown in FIG.
3.
The various components are referenced to a circuit common potential shown as GND.
In FIG.
4, a phaseshift network 1 includes two phaseshift branches and a summer.
Specifically, R1 and C1 implement a -45.
degree.
phaseshift branch or network (P1) for an input signal Q.
sub.
-- MIXER, and thus retard the signal Q.
sub.
-- MIXER by 45.
degree.
.
R2, R3 and C2 implement a +45.
degree.
phaseshift branch or network (P2) for an input signal I.
sub.
-- MIXER, and thus advance the signal I.
sub.
-- MIXER by 45.
degree.
.
Q.
sub.
-- MIXER and I.
sub.
-- MIXER are the output signals of M1 and M2, respectively, of FIG.
3.
R4, R5, and R6 implement a summing circuit (S1), having a summing node (SN).
S1 provides isolation between the two summing inputs at the left terminals of R4 and R5 by providing a high insertion loss
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