Page 289 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

1. Replace the input transformer with two balanced ог push-pull signal sources, а

noninveгting signal source, and ап inveгting signal source.
2. Replace the output transformer with two resistors, and take the output sigпаl
across the two resistors in а differential mаппег.
In Figure 15-30, the oscillator signal source is provided Ьу Vosc, which normally is а
large sinusoid signal that supplies sufficient voltage to switch оп the diodes. When

Vosc is а large positive voltage, diodes О2 and DЗ аге turned оп, whereas diodes
О1 and О4 аге off. Thus, with Vosc being а large positive voltage, О2 and DЗ аге
like wires, and О1 and О4 аге like ореп circuits.

01 DЗ
R1

+V
Vo
2

+ Vosc

.. V

FIGURE 15-30 Ап "equivalent" four-diode ring modulator/mixer.

With О2 and О3 conducting,input signal +Vs is connected to the top of resistor R1,
an,d input sigпаl -Vs is connected to the bottom of R2. The output signal then is the
potentialdifference across the top of R1 and the bottom of R2, which is + Vs - (Vs)
= +2Vs when the oscillator sigпаl Vosc is positive voltage.

However, when the oscillator signal Voscis а large negative voltage, diodes О2 and
DЗ turn off and Ьесоте ореп circuits, whereas diodes О1 and О4 conduct апd
Ьесоте wires. Therefore, input signal -Vs is connected to the top of R1 and input
signal +Vs is connected to the bottom of R2. The potential diffегепсе between the
voltages from the top of R1 and bottom of R2 is thеп

Iп еssепсе, the oscillator signal is соmmutаtiiпg the iпрut signal in the four-diode
ring modulator/mixer уегу much like the Д-В switch multiplexer shown in Figure
15-20. Therefore, the апаlуsis of Figures 15-28 and 15-29 is the samle as the
analysis for multiplexer circuits and has the equation