Page 184 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

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whereas a O.S-degree error from the gO-degree difference phase between the I and
Q channels will result in a 0.435 percent leak-through of the image signal.
For an appropriate approximation of the residual image signal output with a phase

error or deviation from the 90 degree difference between the I and Q channels is 1
percent per 1 degree of phase error, see Chapter 21, which presents an analysis of
an image-reject mixer and provides further details pertaining to phase error.
Mu'ltipliers for Generating 0- and gO-Degree Phases

While the phase-shifting circuit in Figure 12-5 provides an accurate phase
difference of 90 degrees between the I and Q channels, its accuracy depends on
precision parts. Also, to increase the range of frequencies, more amplifier stages

must be added. For example, if a frequency ratio of 500: 1 is needed with less than
0.5 degree of error, 10 amplifiers instead of the 6 shown in Figure 12-5 will be
required.
So an alternative to phase-shifting networks is to use multiplier circuits. Chapters 8
and 9 showed that a mixing circuit creates a multiplying effect on two signals. And

one of the outputs of the mixing circuit is a signal that has a frequency equal to the
difference of the two input signals-the local oscillator signal and the RF signal.
But what if we connect the RF signal to two multipliers, and each multiplier is
connected to an oscillator of the same frequency, and one of the m,ultiplier has a
phase-shifted oscillator signal? See Figure 12-6.