Multiple oscillator modulator circuit

A plurality of oscillator-modulator combinations is incorporated into a monolithic integrated circuit. A single pole multiple position switch is used to energize a single oscillator at a time, and a filter having a plurality of inputs and a common output is coupled to the modulator outputs. The modulators each have a common modulation input. Using this combination, a very simple switch can be used to control the modulated signal output at different carrier frequencies.

BACKGROUND OF THE INVENTION 
The invention has application where it is desired to switch select one of a 
plurality of modulated carrier signals. In the prior art it has been 
common to switch one of a plurality of signal sources to an output 
terminal. Typically, a plurality of tank-circuits, such as crystal 
elements, is connected to a switch and the desired one is coupled to an 
oscillator. The oscillator output is then fed to a modulator, the tuned 
circuit of which is switch selected by an element ganged to the oscillator 
switch. The modulator output is then made up of the modulated component of 
the oscillator signal. This system requires a very complex switch, which, 
with its attendant wiring, tends to produce spurious coupling of unwanted 
signals. Also the switch being remote from the tank circuits means that 
long signal paths must be used and this introduces stray parasitic 
reactances than can adversely affect the behavior of the signal circuits. 
SUMMARY OF THE INVENTION 
It is an object of the invention to incorporate a plurality of 
oscillator-modulator circuits into a monolithic integrated circuit in such 
a way as to permit a simple switch to select one of a plurality of output 
signals wherein the unused circuits do not intrude upon the operative 
circuit. 
It is a further object of the invention to permit one of a plurality of 
oscillator-modulator circuits to be selected and energized to the 
exclusion of the others in a simple switch selected configuration adapted 
for monolithic circuit integration. 
These and other objects are achieved in an integrated circuit that contains 
a separate oscillator-modulator combination for each desired signal 
frequency. A separate tank circuit is employed for each oscillator. A 
simple selector switch energizes only one oscillator of the plurality. The 
oscillator then drives its associated modulator. Each oscillator has a 
signal output that controls a current source coupled to the associated 
modulator, which is thereby turned off when the oscillator is not 
energized. The modulators all have a common modulation signal input and 
each one feeds a separate input of an output filter. The output filter 
contains a plurality of band pass elements, one tuned to each of the 
oscillators, and having a common output port. With this arrangement, when 
the selected oscillator is energized, the related modulator modulates the 
oscillator signal, and the output filter passes the modulated signal while 
rejecting those components outside the filter passband. This system 
permits a very simple switch to select the frequency of the modulated 
output signal with a minimum of spurious responses.

DESCRIPTION OF THE INVENTION 
In FIG. 1 a multichannel system is shown. Two channels are detailed and 
provision is shown for additional oscillator-modulator combinations. As a 
practical matter, any reasonable number could be included and integrated 
into a single microcircuit chip. 
A source of potential is applied between terminals 10 and 11. While not 
shown, this source also supplies potential to various elements within the 
integrated circuit. Switch 12, a single pole, multiple position switch 
applies operating potential to only one of the plurality of oscillators. 
As shown, oscillator 13 will be operative. If desired, switch 12 could be 
operated to energize oscillator 14 or any one of the other oscillators as 
indicated by the dashed lines. All of the oscillators are coupled to a 
common current source 15, which is designed to supply a predetermined 
current to whichever oscillator is energized. Each oscillator has an 
associated modulator connected thereto. For example, modulator 16 is 
coupled to oscillator 13 and modulator 17 is coupled to oscillator 14. 
Each modulator has a common modulation input from terminal 18 and each 
couples its output to a separate input of filter 19.This filter is 
external to the microcircuit chip because it uses either L-C tuned 
filters, ceramic resonators, or the equivalent. This element will be 
custom designed for the particular application. The function of filter 19 
is to combine the outputs of the modulators into a single output on 
terminal 20. Filter 19 is typically a plurality of band pass elements 
having common outputs. Each element is tuned to accept the frequency of 
one of the oscillators and to pass the carrier with its attendant side 
band products. 
Each modulator is operated from a current source. Sources 21 and 22 operate 
modulators 16 and 17 respectively and the sources are switched from the 
respective oscillators 13 and 14. When oscillator 13 is turned on by means 
of being associated with the active terminal of switch 12, it will in turn 
switch on the associated current source 21, thereby energizing modulator 
16. All other oscillators and their associated modulators would therefore 
be deactivated. Accordingly, a very simple switch controls the entire 
circuit without having to switch or interrupt any signal-carrying 
circuits. 
FIG. 2 is a schematic diagram of an integrated circuit employed to 
implement the functions associated with FIG. 1. Those circuit elements 
located above the horizontal line connected to terminal 10 are external to 
the microelectric IC. The circles indicate IC pads which are connected to 
package terminals. The circuit shown contains two oscillator-modulator 
combinations, only one of which is operative at a time, as determined by 
switch 25. Since the switch is shown in its left hand position, only the 
left hand portion of the schematic will be described in detail. The right 
hand portion operates in the same manner. In FIG. 2 the filter 19 of FIG. 
1 is not shown. Its input terminals would be connected to the designated 
output terminals 26 and 27. 
Oscillator 13 is made up of matched transistors 30 and 31 in a balanced 
configuration. The frequency of oscillation is set by L-C tank circuit 32. 
The oscillator operation is taught and claimed in my copending application 
Ser. No. 731,167 titled INTEGRATED CIRCUIT OSCILLATOR and filed Oct. 12, 
1976. 
Resistors 33 and 34 are matched and act as a balanced oscillator load. 
Resistors 35 and 36 are matched and act as base bias resistors. Resistor 
37 couples the oscillator transistor emitters to current source 15 and 
acts to isolate the oscillator and prevent spurious common mode 
oscillation. Zener diodes 38 and 39 are matched, act as the oscillator 
feedback elements, and provide level shifting from collector to base. The 
action of this circuit is detailed in the above-identified application and 
will not be repeated here. 
The paraphase output from oscillator 13 is applied through isolation 
resistors 42 and 43 to emitter follower transistors 40 and 41, which 
couple to balanced quad modulator 44. Transistors 44a, 44b, 44c, and 44d 
are connected into a quad configuration having two base inputs and a 
single output at terminal 26 across load resistor 49. Transistors 40 and 
41 along with resistors 47 and 48 establish the quiescent bias on the base 
input terminals of quad 44. Zener diodes 45 and 46 are conductive when the 
oscillator-modulator combination is turned off as will be described 
hereinafter. It can be seen that as oscillator 13 alternately switches 
transistors 40 and 41, the quad input terminals are alternately pulled 
toward the positive supply potential at terminal 10. Thus the carrier 
signal from oscillator 13 alternately switches the transistor pairs in 
quad 44. Modulation is applied to quad 44 from a pair of current sources 
50 and 51. 
Two modulation inputs are shown at terminals 2 and 53. Signals from 
terminal 52 are applied to transistor 54, which acts with resistor 55 as 
an emitter follower, the output of which is applied to current source 50 
through isolation resistor 56. Signals from terminal 53 are applied to 
transistor 65, which acts with resistor 66 as an emitter follower, the 
output of which is applied to current source 51 through isolation resistor 
67. Current sources 50 and 51 are respectively biased by constant current 
transistors 57 and 58 respectively. Matched resistors 59 and 60 ensure 
that equal currents flow in transistors 57 and 58. The actual current 
value is established by the value of resistor 61 and diode 62. It can be 
seen that parts 57 through 62 comprise a current mirror. When oscillator 
13 is turned on, current will flow from the positive supply terminal 10, 
down through resistors 33 and 34, zener diodes 38 and 39, and resistors 35 
and 36 into diode 62 and resistor 61 back to terminal 11. The potential 
drops across diode 62 and resistor 61 will turn on transistors 57 and 58. 
Thus the current flowing in diode 62 is mirrored as the currents flowing 
in transistors 57 and 58. Resistor 63 couples transistors 50 and 51 
together and is selected in value to minimize spurious modulation products 
in the output of quad 44. Thus current sources 50 and 51 are modulated by 
signals from terminals 52 and 53 respectively. Whichever source is 
modulated, a portion of the modulating signal appears antiphase at the 
other source. 
Since the operation of current source transistors 57 and 58 depended upon 
current flowing through diode 62, a control action is present. If switch 
25 is operated to disable oscillator 13, current flow in diode 62 ceases 
and transistors 57 and 58 turn off. This halts current flow in transistors 
50 and 51, thereby terminating operation of quad 44. Because of zener 
diodes 45 and 46 and resistors 47 and 48, the bases of quad 44 will be 
held at a fixed potential and the emitters of transistors 44a through 44d 
will float and approach this level. The emitters of transistors 50 and 51 
will float at about their base potentials. Therefore, without current flow 
in oscillator 13, the associated modulator is inoperative. 
While FIG. 2 shows two oscillators, 13 and 14, along with associated 
current controlled modulators, and switch 25 energizes one or the other 
oscillator, additional oscillator-modulator combinations could be 
incorporated into particular IC. The switch would be designed to have one 
position per oscillator. 
EXAMPLE 
An IC designed as shown in FIG. 2 was constructed. The following parts list 
details the associated values. While only half of the parts are itemized, 
the parts on the second (right hand) half of the circuit are identical. 
The transistors are all similar and where desired are fabricated in side 
by side matched pairs. The diodes shown are either zener diodes reverse 
biased or they constitute forward biased emitter base transistor diodes. 
______________________________________ 
Part Designation 
Value 
______________________________________ 
Current Source 15 
2 ma 
Tank 32 TV Channel 4 Video Carrier 
(67.25 mhz) 
Resistor 33 240 ohms 
Resistor 34 240 ohms 
Resistor 35 2.7K ohms 
Resistor 36 2.7K ohms 
Resistor 37 1K ohms 
Zener Diode 38 5.6 volts 
Zener Diode 39 5.6 volts 
Resistor 42 250 ohms 
Resistor 43 250 ohms 
Zener Diode 45 7 volts 
Zener Diode 46 7 volts 
Resistor 47 10K ohms 
Resistor 48 10K ohms 
Resistor 49 75 ohms 
Resistor 55 10K ohms 
Resistor 56 250 ohms 
Resistor 59 220 ohms 
Resistor 60 220 ohms 
Resistor 61 100 ohms 
Diode 62 (emitter-base diode) 
Resistor 63 3.6K ohms 
Resistor 66 10K ohms 
Resistor 67 250 ohms 
Tank 70 TV Channel 3 Video Carrier 
(61.25 mhz) 
______________________________________ 
A 15 volt supply was coupled to terminals 10 and 11. The input terminals 53 
and 52 were fed video and chroma subcarrier signals and the modulated 
signals coupled to the antenna terminals of a conventional color TV 
receiver. The TV screen portrayed the video and color modulation 
information and the circuit could be switched to either channel 3 or 
channel 4, using only the simple SPDT switch shown at 25. The modulation 
of the carrier was adequate on each output channel and spurious modulation 
products acceptably low. There was no detectable channel 3 output when the 
switch was positioned as shown. 
the invention has been described and a particular example detailed to show 
an application to television carrier modulation. It is clear that 
alternatives and equivalents will occur to a person skilled in the art. 
Therefore it is intended that the invention be limited only by the 
following claims.