TEMPERATURE STABLE TONE GENERATOR

• US 3,815,050 A
• Filed: 03/23/1973
• Issued: 06/04/1974
• Est. Priority Date: 02/05/1971
• Status: Expired due to Term

• Current Assignee: Michael C.J. Cowpland
• Original Assignee: Michael C.J. Cowpland
• Inventors: Cowpland, Michael C. J.
• Primary Examiner(s): Kominski, John
• Application Number:
  US05/344,238
• Time in Patent Office: 438 Days
• Field of Search: 331/110,135,142
• US Class Current: 331/110
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/26 frequency-determining element being part of bridge circuit in closed ring around which signal is transmitted; frequency-determining element being connected via a bridge circuit to such a closed ring, e.g. Wien-Bridge oscillator, parallel-T oscillator
• CPC Class Codes: H04M 1/50 by generating or selecting currents of predetermined frequencies or combinations of frequencies

Abstract

A temperature stable tone oscillator having advantageous application as a dialing oscillator in telephone sets. An emitter-follower uses a parallel T, R-C filter with greater than unity gain in its feedback loop; a temperature stable clipper limits the signal so as to keep the emitter-follower out of saturation, while additional circuits compensate for temperature variation of the operating point of the emitter-follower, feed large amounts of current to the clipper and its reference source with a small voltage drop, etc; the tone oscillator can thus be used with very low supply voltages.

Claims

1. An oscillator circuit comprising:

a. means for applying operating current to said circuit, b. an emitter follower means having a voltage gain less than unity, and a load, serially connected across the (a) means, c. a parallel T, R-C filter network, having an input terminal, an output terminal, and a ground terminal, the input terminal being connected to the junction of the load and the emitter follower means, and the output terminal being connected to the input of the emitter follower means, said network having a voltage gain greater than 1.0 and less than 1.2, the combined voltage gain of said filter network and the emitter follower means and load being equal to or greater than unity at the resonant frequency of said filter network, the filter network having an input impedance not less than about 15 times the impedance of the load, and an output impedance 1 percent or less than the input impedance of the emitter follower means, d. means for connecting the ground terminal to alternating current ground, and e. clipping means connected to the output terminal of said filter network, having a conduction threshold of such level as to limit the amplitude of a signal at the filter output terminal to a level lower than that which would drive the emitter follower into saturation, comprising a voltage source means for supplying a stable voltage difference between a positive terminal and a negative terminal;

means for clamping a first junction point to a predetermined voltage lower than that at the positive terminal;

means for clamping a second junction point to a predetermined voltage higher than that at the negative terminal;

a pair of diode means serially and unidirectionally connected between the first and second junction points, the cathode and anode of the pair being connected to the first and second junction points respectively;

the predetermined voltages each being about equal to the thresholds of conduction voltages across each of the diode means;

the junction of the pair of diode means being connected, through means for blocking direct current, to the output terminal of said filter network; and

a reference thresholdlevel-raising diode means connected between the (a) means and the negative terminal in the same polarity sense as the baseemitter junction diode of the emitter follower means, both said latter diode and the reference threshold-level-raising diode means having similar thresholds of conduction.

2. A circuit as defined in claim 1, further comprising a voltage divider connected between the positive and negative terminal, having an output voltage tap, the output voltage tap being connected to the ground terminal of said filter network, the voltage at said tap being of predetermined value such as to bias the emitter follower means to a value intermediate its off and saturation levels.

3. A circuit as defined in claim 2, in which the (a) means is comprised of a positive junction point and a negative junction point, further including bias current supply means comprising a supply transistor means having a base, an emitter, and a collector, the collector being connected to the positive junction point, the emitter being connected through an emitter load resistor to said positive terminal;

and a pair of serially and unidirectionally connected diodes connected between said base and said positive terminal, said pair of diodes being poled in the same sense as the base-emitter diode junction of the supply transistor means;

the emitter follower means comprising first, third and fourth transistor means of one polarity type, and a second transistor means of a second polarity type, each having a base, an emitter, and a collector;

the emitters of the First and fourth transistor means being connected together to the load, the collector of the first transistor means to the base of the second transistor means, the collector of the second transistor means to the base of the third transistor means, and the emitter of the third transistor means to the base of the fourth transistor means;

a first biasing resistor connected between the collector of the second transistor means and the load, and the second biasing resistor connected between the emitter of the third transistor means and the load;

the emitter of the second transistor means being connected to the base of the supply transistor means, and the collector of the third transistor means being connected to the emitter of the supply transistor means;

the collector of the fourth transistor means being connected to said positive junction point, and the load terminal which is not connected to the fourth transistor means being connected to said negative junction point;

the first, third, fourth, fifth, sixth, eighth, and supply transistors being of NPN polarity type, and the second and seventh transistor means being of PNP polarity type;

the voltage gain of the filter network being 1.03 + or -2 percent, and having a Q of less than 0.15;

the amplifier having a current gain of about 106;

said filter network having an input impedance of about 15 times the impedance of the load, and an output impedance 1 percent or less than the input impedance of the emitter follower means.

4. An oscillator circuit comprising:

a. means for applying operating current to said circuit, b. an emitter follower means having a voltage gain less than unity, and a load, serially connected across the (a) means, c. a parallel T, R-C filter network, having an input terminal, an output terminal, and a ground terminal, the input terminal being connected to the junction of the load and the emitter follower means, and the output terminal being connected to the input of the emitter follower means, said network having a voltage gain greater than 1.0 and less than 1.2 and a Q of less than 0.15, the combined voltage gain of said filter network and the emitter follower means and load being equal to or greater than unity at the resonant frequency of said filter network, the filter network having an input impedance not less than about 15 times the impedance of the load, and an output impedance 1 percent or less than the input impedance of the emitter follower means, d. means for connecting the ground terminal to alternating current ground, e. clipping means connected to the output terminal of said filter network, having a conduction threshold of such level as to limit the amplitude of a signal at the filter output terminal to a level lower than that which would drive the emitter follower into saturation, and f. means for providing X milliamperes of bias current to the oscillator, connected between one of the pair of input terminals and the oscillator, having an effective internal impedance of Y ohms, and an internal voltage drop of less than 1/3 xy.

5. A circuit as defined in claim 4, further including means connected between the clipping means and said oscillator for varying the threshold of clipping level similarly as the change of conduction threshold level of said oscillator circuit with change of temperature.

6. An oscillator circuit comprising:

a. means for applying operating current to said circuit, b. an emitter follower means having a voltage gain less than unity, and a load, serially connected across the (a) means, c. a parallel T, R-C filter network, having an input terminal, an output terminal, and a ground terminal, the input terminal being connected to the junction of the load and the emitter follower means, and the output terminal being connected to the input of the emitter follower means, said network having a voltage gain greater than 1.0 and less than 1.2, the comBined voltage gain of said filter network and the emitter follower means and load being equal to or greater than unity at the resonant frequency of said filter network, having an input impedance not less than about 15 times the impedance of the load, and an output impedance 1 percent or less than the input impedance of the emitter follower means, d. means for connecting the ground terminal to alternating current ground, e. clipping means connected to the output terminal of said filter network, having a conduction threshold of such level as to limit the amplitude of a signal at the filter output terminal to a level lower than that which would drive the emitter follower into saturation, f. means for providing X milliamperes of bias current to the oscillator, connected between one of a pair of input terminals and the oscillator, having an effective internal impedance of Y ohms, and an internal voltage drop of less than 1/3 xy, g. means connected between the clipping means and the emitter follower means for varying the threshold of the clipping level similarly as the change of conduction threshold level of the emitter follower means with change of temperature, and h. a constant voltage reference connected to the clipping means comprising a current input terminal;

the means for providing bias current comprising a supply transistor having a base, and an emitter, and a collector, the collector being connected to one of the input terminals, an emitter load connecting the emitter to the current input terminal of the constant voltage reference, a pair of serially and unidirectionally connected diodes connected between the input terminal and the base, and a current supply resistor connected between the base and the collector.

7. A circuit as defined in claim 2, further including:

i. a second emitter follower means similar to the first-defined emitter follower means, and a second load, similar to the first-defined load, serially connected across the (a) means;

ii. a second parallel T, R-C filter network with the resonance point different from the resonance point of the first-defined filter network, having an input terminal, an output terminal, and a ground terminal, the input terminal being connected to the junction of the second load and the second emitter follower means, the output terminal being connected to the input of the second emitter follower means, and the ground terminal being connected to said tap; and

iii. a second pair of diode means similar to the first-defined pair of diode means serially and unidirectionally connected between said first and second junction points in the same conduction sense as the first-defined pair of diode means;

iv. the junction of the second pair of diode means being connected, through a second means for blocking direct current, to the output terminal of said filter network;

v. the combined voltage gain of said second filter network and the second emitter follower means and second load being equal to the combined voltage gain of said first-defined filter network and emitter follower means and load at the resonant frequency of said second filter network.

8. An oscillator circuit comprising:

a. means for applying operating current to said circuit, b. an emitter follower having a voltage gain of about 0.99, and a load, serially connected across the (a) means, c. a parallel T, R-C filter network, having an input terminal, an output terminal, and a ground terminal, the input terminal being connected to the junction of the load and the emitter follower means, and the output terminal being connected to the input of the emitter follower means, said network having a voltage gain of 1.03 + or - 2 percent and a Q of less than 0.15, the combined voltage gain of said filter network and the emitter follower means and load being equal to or greater than unity at the resonant frequency of said filter network, the filter network having an input impedance not Less than about 15 times the impedance of the load, and an output impedance 1 percent or less than the input impedance of the emitter follower means, d. means for connecting the ground terminal to alternating current ground, e. said network comprising a first capacitor connected to the input terminal and a first resistor connected between the first capacitor and the output terminal;

a second resistor connected to the input terminal and a second capacitor connected between the second resistor and the output terminal; and

a third capacitor connected between the junction of the second resistor and the second capacitor, and the ground terminal; and

a third resistor connected between the junction of the first capacitor and first resistor, and the ground terminal, f. means for varying the resistance of the third resistor of said filter network such that the resonant and oscillation frequency thereof may be changed, and g. clipping means connected to the output terminal of said filter network, having a conduction threshold of such level as to limit the amplitude of a signal at the filter output terminal to a level lower than that which would drive the emitter follower into saturation.

9. A circuit as defined in claim 1, further comprising a diode bridge connected to said (a) means, having a pair of input terminals for connection to a telephone line having a current supply of any polarity, and a pair of output terminals connected so as to supply positive line current to the terminal of the (a) means connected to the emitter follower means, and negative line current to the terminal of the (a) means connected to the load.