Matrix circuit of FM stereo multiplex demodulation circuit

DETAILED DESCRIPTION An object of this invention is to provide a matrix circuit of an FM-stereo multiplex demodulation circuit in which an FM-demodulated composite signal can be supplied to a switching decoder by shunting an input current corresponding to the FM-demodulated composite signal in a preset ratio even when the FM-demodulated composite signal is a current output and input in the form of current.
According to this invention, there is provided a matrix circuit comprising a first resistor (R.
sub.
A) having one end connected to receive a current signal and another end connected to a first output node (51); a second resistor (R.
sub.
B) having one end connected to said one end of first resistor (R.
sub.
A); a first bipolar transistor (Q3) having a first collector connected to the another end of said second resistor (R.
sub.
B), a first emitter connected to a circuit ground (GND) and a first base connected to said first collector; and a second bipolar transistor (Q4) having a second collector connected to a second output node (52), a second emitter connected to said circuit ground (GND) and a second base connected to said first base.
With the above construction, the other end of each of the resistors (R.
sub.
A) and (R.
sub.
B) as viewed from a current signal supplied from a tone controller is a low impedance.
Therefore, an input current is divided into shunt currents .
DELTA.
i.
sub.
A and .
DELTA.
i.
sub.
B depending on the resistance ratio of the first resistor (R.
sub.
A) and second resistor (R.
sub.
B).
At this time, the shunt current .
DELTA.
i.
sub.
B flowing in the second resistor (R.
sub.
B) is derived with a phase opposite to that of the collector current .
DELTA.
i.
sub.
A of the first bipolar transistor (Q1).
Therefore, it becomes possible to derive shunt currents with opposite phases from the matrix circuit and to supply the same to the switching decoder.
As a result, it becomes possible to supply the current signal from the tone controller directly to the matrix circuit without passing the same through the I/V converter