CA1067589A - Tracking oscillator and use of the same in a frequency to voltage converter - Google Patents
Tracking oscillator and use of the same in a frequency to voltage converterInfo
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- CA1067589A CA1067589A CA274,140A CA274140A CA1067589A CA 1067589 A CA1067589 A CA 1067589A CA 274140 A CA274140 A CA 274140A CA 1067589 A CA1067589 A CA 1067589A
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Abstract
A TRACKING OSCILLATOR AND USE OF THE SAME
IN A FREQUENCY TO VOLTAGE CONVERTER
ABSTRACT
A tracking oscillator includes an integrator and a hysteresis switch for tracking an input train of waves and providing an output train of square waves. The output is fed back to the integrator to mark transitions between increasing and decreasing direction of integration in response to changes between a high and a low level in the output train of square waves. The tracking oscillator is interposed between a limiter and a phase detector and is used to introduce phase delay to the output of the limiter.
The phase detector compares the output of the tracking oscillator and the output of the limiter to provide an output square wave train having a pulse width proportional to the phase delay introduced by the tracking oscillator. A
suitable circuitry, such as a low pass filter and averaging circuitry, is coupled to the output of the phase detector for converting the train of square waves into a DC output r wherein the DC voltage is proportional to the phase delay.
IN A FREQUENCY TO VOLTAGE CONVERTER
ABSTRACT
A tracking oscillator includes an integrator and a hysteresis switch for tracking an input train of waves and providing an output train of square waves. The output is fed back to the integrator to mark transitions between increasing and decreasing direction of integration in response to changes between a high and a low level in the output train of square waves. The tracking oscillator is interposed between a limiter and a phase detector and is used to introduce phase delay to the output of the limiter.
The phase detector compares the output of the tracking oscillator and the output of the limiter to provide an output square wave train having a pulse width proportional to the phase delay introduced by the tracking oscillator. A
suitable circuitry, such as a low pass filter and averaging circuitry, is coupled to the output of the phase detector for converting the train of square waves into a DC output r wherein the DC voltage is proportional to the phase delay.
Description
This invention relates to a tracking oscillator and, more particularly, an improved tracking oscillator and use of the tracking oscillator in a frequency-to-voltage converter.
BACKGROUND OF THE INVENTION
In many RF communications area, it is often necessary to track change over in the frequency of signals relative to a reference frequency in incoming signals~ According to the prior art, phase locked loops are often used for this purpose. The prior art phase locked loop circuitry are, however, usually complex and require a large number of elements which are costly. Prior art frequency-to-voltage converters such as FM discriminators usually use a wide variety of such phase locked loop circuitry or a network of analog filters which are generally complex and costly.
:
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved tracking oscillator.
It is still another object of the present invention to provide less costly and less complex tracking os,cillator.
It is yet another object of the present invention to provide an improved frequency-to-voltage converter using a simplified and improved tracking oscillator.
The foregoing and other objects are achieved in accordance with the present invention by providing a tracking oscillator that includes an integrator and a hysteresis switch connected in series wherein the output of the switch is fed back to the integrator for marking the change of direction of inte-gration, i.e., decreasing or increasing direction as the . ,:
., .
BACKGROUND OF THE INVENTION
In many RF communications area, it is often necessary to track change over in the frequency of signals relative to a reference frequency in incoming signals~ According to the prior art, phase locked loops are often used for this purpose. The prior art phase locked loop circuitry are, however, usually complex and require a large number of elements which are costly. Prior art frequency-to-voltage converters such as FM discriminators usually use a wide variety of such phase locked loop circuitry or a network of analog filters which are generally complex and costly.
:
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved tracking oscillator.
It is still another object of the present invention to provide less costly and less complex tracking os,cillator.
It is yet another object of the present invention to provide an improved frequency-to-voltage converter using a simplified and improved tracking oscillator.
The foregoing and other objects are achieved in accordance with the present invention by providing a tracking oscillator that includes an integrator and a hysteresis switch connected in series wherein the output of the switch is fed back to the integrator for marking the change of direction of inte-gration, i.e., decreasing or increasing direction as the . ,:
., .
- 2 ~
. .
~067589 input train of waves traverses back and forth between a lower and a higher voltage and introduce phase delay in the output train of waves.
In accordance with another aspect of the present inven-tion, the aforementioned tracking oscillator is advantageously used in a frequency-to-voltage converter by interposing the tracking oscillator between a limiter and a phase detector.
The tracking oscillator provides a phase delay and the phase detector measures the phase delay by comparing the output of the tracking oscillator with the output of the limiter. The output of the phase detector is in the form of a train of waves with pulse width proportional to the phase delay introduced by the tracking oscillator. The output of the phase detector may be advantageously converted into a DC
voltage proportional to the phase delay, that is, propor-tional to the pulse width of the phase detector, by using a suitable circuitry, such as a low pass filter and an averaging circuit.
:~
The foregoing and other objects and features of the present invention will be more clearly understood from the - following detailed description of an illustrative embodiment of the present invention in conjunction with the accompanying drawings, ,1 BRIEF DESCRIPTION OF THE DRAWINGS
_ _ Figure 1 shows an embodiment of a tracking oscillator and use of the tracking oscillator in a frequency to voltage converter in accordance with the present invention.
, Figure 2 shows typical waveforms of the frequency to voltage converter operating in a steady state.
;
, Figure 3 shows steady state waveforms of the tracking oscillator in a free running mode using an inverting integrator.
Figure 4 shows steady state waveforms of the tracking oscillator in the tracking mode using an inverting integrator wherein the output voltage of the hysteresis switch has greater weight than the input voltage to the integrator.
Figure 5 shows waveforms of the tracking oscillator shown in Figure 4 after they have been adjusted for symmetri-cal voltage swings.
DETAILED DESCRIPTION
Figure 1 shows a frequency-to-voltage converter in a functional block diagram form that embodies the present invention. Figure 2 shows timing waveforms of the frequency-to-voltage converter that are helpful in understanding the operation of the frequency to voltage converter Referring to Figures 1 and 2, an input signal may be either a sinusoid S or a square wave A, as illustrated in Figure 2. A suitable conventional limiter 10 can be used, if required, to square ; the input signal by amplifying and clipping the input to provide a square wave B of a desired amplitude and polarity as shown in Figure 2.
The output of the limiter is applied to a tracking oscillator 13 comprising an integrator 21 and an hysteresis switch 23 coupled in series as shown in Figure 1. An output of the hysteresis loop is fed back to the integrator. The I integrator is also adapted to receive two inputs; one from t! the limiter and the other from the output of the hysteresis switch. The output of the hysteresis switch is used to , provide a reference signal C, with a phase inversion, as ,1 .
.. ., ~ ~ -. .. . . .;,.. , ~ ,. ,, .. . .. : .: .
10~7S89 desired, with respect to the square wave input B, as shown.
If necessary, the hysteresis switch can be adapted to provide reference signals without a phase inversion. The tracking oscillator 13 produces a square wave output D of the same frequency as its input signal B, but shifted in phase with respect to it. As shown this phase shift is directly propor-tional tG the difference in frequency between the nominal, that is, free running frequency of the tracking oscillator 13 and the frequency of the input singal S or A. A phase detector 15 is coupled to receive the phase shifted output D
from the tracking oscillator to produce, as its output signal, a pulse train E whose pulse width is directly propor-tional to the phase shift.
A suitable circuitry~ such as a low pass filter/averaging circuit 17 is coupled to the phase detector to provide an output signai F which is directly proportional to the frequency shift defined above and which may range within a maximum VmaX~ and a minimum, Vmin.
Referring to Figure 1 again, an aspect of the present invention is the tracking oscillator 13 used in the frequency-; to-voltage converter, as illustrated in Figure 1. The tracking oscillator includes the integrator 21 and the hysteresis switch 23 connected in series. The oscillator is designed so that in a steady state operation, it exhibits the characteristics as illustrated in the waveforms shown in Figures 2 and 3. In the absence of an input signal from the limiter 10~ the tracking oscillator operates as a free running oscillator. The integrator 21, as illustrated, is an inverting integrator, although the integrator need not be an inverting integrator. The operation of the tracking ~. j i :;
~ ~ CM-76799 ~0~7589 oscillator will be described with reference to the inverting integrator shown.
1. Refer to Figures 1, 2 and 3. At an arbitrary time, T=Q, assume the tracking oscillator is at a steady state condition.
2. With the instantaneous voltage of-the output of the hysteresis switch 23 ~Fig. 2,V and Fig. 3, Vc) just switched to Va and with the output voltage, VOUt (~ig. 3) applied to the hysteresis switch to a voltage Vc, the output voltage VOUt~ of the integrator will then decrease linearly with time from a voltage Vc to a voltage Vd. If a non-inverting integrator were used, Vc and Vd would be inter-changed and the polarity of the voltage transitions of the . . .
voltage output, VOUt, of the integrator is reversed. -
. .
~067589 input train of waves traverses back and forth between a lower and a higher voltage and introduce phase delay in the output train of waves.
In accordance with another aspect of the present inven-tion, the aforementioned tracking oscillator is advantageously used in a frequency-to-voltage converter by interposing the tracking oscillator between a limiter and a phase detector.
The tracking oscillator provides a phase delay and the phase detector measures the phase delay by comparing the output of the tracking oscillator with the output of the limiter. The output of the phase detector is in the form of a train of waves with pulse width proportional to the phase delay introduced by the tracking oscillator. The output of the phase detector may be advantageously converted into a DC
voltage proportional to the phase delay, that is, propor-tional to the pulse width of the phase detector, by using a suitable circuitry, such as a low pass filter and an averaging circuit.
:~
The foregoing and other objects and features of the present invention will be more clearly understood from the - following detailed description of an illustrative embodiment of the present invention in conjunction with the accompanying drawings, ,1 BRIEF DESCRIPTION OF THE DRAWINGS
_ _ Figure 1 shows an embodiment of a tracking oscillator and use of the tracking oscillator in a frequency to voltage converter in accordance with the present invention.
, Figure 2 shows typical waveforms of the frequency to voltage converter operating in a steady state.
;
, Figure 3 shows steady state waveforms of the tracking oscillator in a free running mode using an inverting integrator.
Figure 4 shows steady state waveforms of the tracking oscillator in the tracking mode using an inverting integrator wherein the output voltage of the hysteresis switch has greater weight than the input voltage to the integrator.
Figure 5 shows waveforms of the tracking oscillator shown in Figure 4 after they have been adjusted for symmetri-cal voltage swings.
DETAILED DESCRIPTION
Figure 1 shows a frequency-to-voltage converter in a functional block diagram form that embodies the present invention. Figure 2 shows timing waveforms of the frequency-to-voltage converter that are helpful in understanding the operation of the frequency to voltage converter Referring to Figures 1 and 2, an input signal may be either a sinusoid S or a square wave A, as illustrated in Figure 2. A suitable conventional limiter 10 can be used, if required, to square ; the input signal by amplifying and clipping the input to provide a square wave B of a desired amplitude and polarity as shown in Figure 2.
The output of the limiter is applied to a tracking oscillator 13 comprising an integrator 21 and an hysteresis switch 23 coupled in series as shown in Figure 1. An output of the hysteresis loop is fed back to the integrator. The I integrator is also adapted to receive two inputs; one from t! the limiter and the other from the output of the hysteresis switch. The output of the hysteresis switch is used to , provide a reference signal C, with a phase inversion, as ,1 .
.. ., ~ ~ -. .. . . .;,.. , ~ ,. ,, .. . .. : .: .
10~7S89 desired, with respect to the square wave input B, as shown.
If necessary, the hysteresis switch can be adapted to provide reference signals without a phase inversion. The tracking oscillator 13 produces a square wave output D of the same frequency as its input signal B, but shifted in phase with respect to it. As shown this phase shift is directly propor-tional tG the difference in frequency between the nominal, that is, free running frequency of the tracking oscillator 13 and the frequency of the input singal S or A. A phase detector 15 is coupled to receive the phase shifted output D
from the tracking oscillator to produce, as its output signal, a pulse train E whose pulse width is directly propor-tional to the phase shift.
A suitable circuitry~ such as a low pass filter/averaging circuit 17 is coupled to the phase detector to provide an output signai F which is directly proportional to the frequency shift defined above and which may range within a maximum VmaX~ and a minimum, Vmin.
Referring to Figure 1 again, an aspect of the present invention is the tracking oscillator 13 used in the frequency-; to-voltage converter, as illustrated in Figure 1. The tracking oscillator includes the integrator 21 and the hysteresis switch 23 connected in series. The oscillator is designed so that in a steady state operation, it exhibits the characteristics as illustrated in the waveforms shown in Figures 2 and 3. In the absence of an input signal from the limiter 10~ the tracking oscillator operates as a free running oscillator. The integrator 21, as illustrated, is an inverting integrator, although the integrator need not be an inverting integrator. The operation of the tracking ~. j i :;
~ ~ CM-76799 ~0~7589 oscillator will be described with reference to the inverting integrator shown.
1. Refer to Figures 1, 2 and 3. At an arbitrary time, T=Q, assume the tracking oscillator is at a steady state condition.
2. With the instantaneous voltage of-the output of the hysteresis switch 23 ~Fig. 2,V and Fig. 3, Vc) just switched to Va and with the output voltage, VOUt (~ig. 3) applied to the hysteresis switch to a voltage Vc, the output voltage VOUt~ of the integrator will then decrease linearly with time from a voltage Vc to a voltage Vd. If a non-inverting integrator were used, Vc and Vd would be inter-changed and the polarity of the voltage transitions of the . . .
voltage output, VOUt, of the integrator is reversed. -
3, When the voltage output, VOUt~ reaches the lower hysteresis voltage Vd, at time To~ the hysteresis switch 23 will change its output state, so that its output voltage, namely, Fig. 2; C: Fig. 3; Vc applied to t~e input of the integrator and its output ~Fig. 2;B) applied to the phase detector 15 are switched.
4, This transition of the output of the hysteresis switch from Va to Vb reverses the slope of the output signal, VOUt~ of the integrator 21 so that the output, VOUt, will rise linearly from voltage Vd to voltage Vc~ during the interval from To to 2To-~ 5. When the output, VOUt of the integrator reaches the i upper hysteresis voltage limit Vc at time 2To, the hysteresis ~l switch 23 will change back to its previous state, so that .1. .
I its output voltage- (Fig. 2;D) switch back.
.
6. The steps 2 through S hereinabove are repeated cyclically, The resulting free running oscillator has a frequency fO = 2To 106~589 Now suppose an input is applied to the limiter and the input is such that the limiter produces a square wave at the output thereof as illustrated in Figure 2A and suppose further that it swings symmetrically above and below the integrator reference voltage, V f = 2- - This will modify the integrator output waveform as illustrated in Figure 4. As described hereinbelow in detail, with the inverting integrator, the output of the hysteresis switch 23 (Fig. 2;D) has greater influence on phase detector 15 than the voltage Fig. 2;A applied to the integrator from the limiter.
1. Assume that the tracking oscillator has been ; operating under the foregoing conditions for a sufficient time to achieve a steady state operation.
2. During the interval from time a to ~T, the voltage output of the limiter, Fig. 2, B~ is equal to Valt the feedback voltage from the hysteresis switch is equal to Vb'.
Therefore the integrator output voltage, VOUt' will increase linearly with its larger positive slope.
3. At time ~T, the voltage output of the integrator VOUt' will reach Vcl, causing the hysteresis switch 23 to change its state and switching its output from Vb' to Val.
4 During the interval from ~T to T the oscillator input voltage is equal to Ve and the output voltage of the hysteresis switch is equal to Va', Therefore, the output of the integrator, VOUt, will decrease linearly with smaller negative slope.
I its output voltage- (Fig. 2;D) switch back.
.
6. The steps 2 through S hereinabove are repeated cyclically, The resulting free running oscillator has a frequency fO = 2To 106~589 Now suppose an input is applied to the limiter and the input is such that the limiter produces a square wave at the output thereof as illustrated in Figure 2A and suppose further that it swings symmetrically above and below the integrator reference voltage, V f = 2- - This will modify the integrator output waveform as illustrated in Figure 4. As described hereinbelow in detail, with the inverting integrator, the output of the hysteresis switch 23 (Fig. 2;D) has greater influence on phase detector 15 than the voltage Fig. 2;A applied to the integrator from the limiter.
1. Assume that the tracking oscillator has been ; operating under the foregoing conditions for a sufficient time to achieve a steady state operation.
2. During the interval from time a to ~T, the voltage output of the limiter, Fig. 2, B~ is equal to Valt the feedback voltage from the hysteresis switch is equal to Vb'.
Therefore the integrator output voltage, VOUt' will increase linearly with its larger positive slope.
3. At time ~T, the voltage output of the integrator VOUt' will reach Vcl, causing the hysteresis switch 23 to change its state and switching its output from Vb' to Val.
4 During the interval from ~T to T the oscillator input voltage is equal to Ve and the output voltage of the hysteresis switch is equal to Va', Therefore, the output of the integrator, VOUt, will decrease linearly with smaller negative slope.
5. At time T ~ the oscillator input voltage B changes from Ve to Vh tFig. 4). Thus, during the interval from T to '~ 30 T + ~T the drive voltage Vh is equal to the switch voltage ~' -7-':: . ' .: :
lOG75t39 output Va. Therefore, the output of the integrator VOUt will decrease linearly with its larger negative slope.
lOG75t39 output Va. Therefore, the output of the integrator VOUt will decrease linearly with its larger negative slope.
6. At time T + ~T, the integrator output will reach Vd', Vd' causing the hysteresis switch to change its output from Va to Vb -
7. During the interval from T ~ QT to 2T, the oscilla-tor input is at Vh and the switch voltage reference signal is Vb'. Therefore, the output of the integrator VOUt will increase linearly with its smaller positive slope.
8. At time 2T, the oscillator input voltage changes from Vh to Ve and the steps 2 through 8 described hereinabove are repeated.
The result of the operation described above is to generate a signal at the output (Fig. 2; D) of the hysteresis switch 23, which is of the same frequency as the driving signal applied to the tracking oscillator at the limiter.
In addition, the output of the switch is inverted and shifted to the right by ~T. ~T iS dependent on the frequency of the oscillator input (Fig. 2; B) and the ratio of the two resistors Rl and R2 in the integrator 21. In fact, it is found that the phase shift ~f, that is, the difference between the free running frequency and the frequency of the osci:Llator input signal, B, i9 directly proportional to ~T and to the ratio of the two resistors Rl and R2.
The tracking oscillator will operate according to the ; same principle whether the integrator is inverting or non-inverting, whether the influence of the switch output is greater than, equal to, or less than the influence of the input~ In practice, it was found that the inverting integra-tor was found easier and less costly to implement. Also, it .. : - 8 -1C~67589 was found that the transfer ratio of the frequency to voltage converter is proportional to the ratio of the influence of the output voltage, C, of the hysteresis switch to that of the input drive voltage B so that influence of the switch output would usually be chosen equal to or greater than that of the input voltage B.
The phase detector 15 operates as follows. The detector produces a pulse train whose pulse width is proportional to ~T. Referring to Figure 2, note that the two input signals, one from the output of the tracking oscillator (Figure 2;D) and the other from the output of the limiter (Fig. 2;D) are applied to the phase detector. The oscillator output is phase shifted by virtue of the behavior of the tracking oscillator as described hereinabove. The resulting output signals of the phase detector shown in Figure 2;E. The detector output is a pulse train wherein a pulse appears whenever the two input signals are at different voltage levels. This can be achieved by an Exclusive-OR gate. An Exclusive-OR gate is inexpensive and small. However, other suitable means may be used in place of the Exclusive-OR
gate.
The present tracking oscillator can be advantageously used in a frequency-to-voltage converter. This i~ readily accomplished by applying the output of the phase detector 15 to a suitable circuit, such as a conventional low pass filter/averaging circuit 17 and adapted to provide DC
voltage proportional to the pulse width ~T. If the frequency of the input signal to the frequency to voltage converter is varying at the slower rate than the frequency of the tracking oscillator itself~ then the low pass filter provides an "
" ' . g _ - - ; : : ~ . ,- , .: : . , , -1~67589 output voltage which varies in direct proportion to the input signal frequency. In such a case, the converter functions as an FM discriminator. If the input voltage shifts between the two frequencies, then the converter functions as frequency shift key detector.
Tracking oscillator 13 shown in Figure 1 and the overall circuit configuration of the frequency-to-voltage converter shown in Figure 1 may be advantageously implemented in a ; large scale integrated circuit form. The limiter 10 may include a three stage inverter of CMOS gates connected in series in a conventional manner (not shown). The output of the second gate may be applied to the phase detector and may be used to provide a phase inversion with respect to the ; output of the third gate applied to the tracking oscillator 21. The integrator 21 comprises a CMOS gate G6, a capacitor C7, resistors Rl, R2, and R3 as schematically shown and connected. The hysteresis switch 23 includes CMOS gates G7 through GlQ and resistors R8, R9, R10, connected, as illus-trated to form the tracking oscillator 23. The transfer ratio of the frequency to voltage converter is proportional to the ratio Rl + R2 . The maximum and minimum hysteresis voltages, Vc' and Vd' are determined by the ratio of the ~ resistances of the resistors, R3 and R10. The phase shifted ; output of the hysteresis switch 23 of the tracking oscillator is taken from the output of CMOS gate G9 to provide the desired polarity of the frequency-to-voltage transfer ratio.
The phase detector 15 may include an Exclusive-OR gate Gll. The low pass filter/averaging circuit 9 may contain an inverter and two active second order bypass low filters in series ~not shown) of a conventional design.
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:
, .
CM-76799 1~67S89 The reference Yoltage Rref may be maintained throughout the circuit at the threshold voltage of the CMOS gates and the voltage swings are symmetrical above and below the threshold voltage, as illustrated in Fig. 5~ This is accom-plished using negative eedback around various gates. This factor accounts for the use of various circuit components such as resistors R3, R8, R9, and gate Gl0 in the tracking oscillator and similar elements that may be used in the low pass filter and averaging circuit 17. In accordance with an aspect of the present invention, the tracking oscillator and the remaining circuit elements can be readily implemented by using conventional CMOS integrated circuits, capacitors and resistors and can be readily made in a hybrid circuit.
In summary, then, the present invention provides a tracking oscillator of a greatly simplified circuitry and novel utilization of such a tracking circuitry in combination with a limiter and a phase detector for providing a frequency-,.
to-voltage converter, The converter may be advantageously used as an FM discriminator, or frequency shift keying circuit as desired~ These features of the invention are shown implemented in the form of low cost CMOS integrated circuits. The overall frequency-to-voltage converter circuitry can be readily implemented essentially in two CMOS integrated circuits: one to include the limiter and tracking oscillator and the other to include the phase detector and the low pass filter and averaging circuit~ Each of these CMOS integrated circuits can be implemented with a single low cost digital ; integrated circuit.
Since C~OS integrated circuits are low cost elements, cost savings for tne overall circuitry is very significant.
. CM-76799 1~67589 Moreover, the use of the limited number of small circuit components renders the circuit more reliable. Also the present circuit is more suitable for implementation as a hybrid circuit than the prior art frequency-to-voltage converter circuits.
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The result of the operation described above is to generate a signal at the output (Fig. 2; D) of the hysteresis switch 23, which is of the same frequency as the driving signal applied to the tracking oscillator at the limiter.
In addition, the output of the switch is inverted and shifted to the right by ~T. ~T iS dependent on the frequency of the oscillator input (Fig. 2; B) and the ratio of the two resistors Rl and R2 in the integrator 21. In fact, it is found that the phase shift ~f, that is, the difference between the free running frequency and the frequency of the osci:Llator input signal, B, i9 directly proportional to ~T and to the ratio of the two resistors Rl and R2.
The tracking oscillator will operate according to the ; same principle whether the integrator is inverting or non-inverting, whether the influence of the switch output is greater than, equal to, or less than the influence of the input~ In practice, it was found that the inverting integra-tor was found easier and less costly to implement. Also, it .. : - 8 -1C~67589 was found that the transfer ratio of the frequency to voltage converter is proportional to the ratio of the influence of the output voltage, C, of the hysteresis switch to that of the input drive voltage B so that influence of the switch output would usually be chosen equal to or greater than that of the input voltage B.
The phase detector 15 operates as follows. The detector produces a pulse train whose pulse width is proportional to ~T. Referring to Figure 2, note that the two input signals, one from the output of the tracking oscillator (Figure 2;D) and the other from the output of the limiter (Fig. 2;D) are applied to the phase detector. The oscillator output is phase shifted by virtue of the behavior of the tracking oscillator as described hereinabove. The resulting output signals of the phase detector shown in Figure 2;E. The detector output is a pulse train wherein a pulse appears whenever the two input signals are at different voltage levels. This can be achieved by an Exclusive-OR gate. An Exclusive-OR gate is inexpensive and small. However, other suitable means may be used in place of the Exclusive-OR
gate.
The present tracking oscillator can be advantageously used in a frequency-to-voltage converter. This i~ readily accomplished by applying the output of the phase detector 15 to a suitable circuit, such as a conventional low pass filter/averaging circuit 17 and adapted to provide DC
voltage proportional to the pulse width ~T. If the frequency of the input signal to the frequency to voltage converter is varying at the slower rate than the frequency of the tracking oscillator itself~ then the low pass filter provides an "
" ' . g _ - - ; : : ~ . ,- , .: : . , , -1~67589 output voltage which varies in direct proportion to the input signal frequency. In such a case, the converter functions as an FM discriminator. If the input voltage shifts between the two frequencies, then the converter functions as frequency shift key detector.
Tracking oscillator 13 shown in Figure 1 and the overall circuit configuration of the frequency-to-voltage converter shown in Figure 1 may be advantageously implemented in a ; large scale integrated circuit form. The limiter 10 may include a three stage inverter of CMOS gates connected in series in a conventional manner (not shown). The output of the second gate may be applied to the phase detector and may be used to provide a phase inversion with respect to the ; output of the third gate applied to the tracking oscillator 21. The integrator 21 comprises a CMOS gate G6, a capacitor C7, resistors Rl, R2, and R3 as schematically shown and connected. The hysteresis switch 23 includes CMOS gates G7 through GlQ and resistors R8, R9, R10, connected, as illus-trated to form the tracking oscillator 23. The transfer ratio of the frequency to voltage converter is proportional to the ratio Rl + R2 . The maximum and minimum hysteresis voltages, Vc' and Vd' are determined by the ratio of the ~ resistances of the resistors, R3 and R10. The phase shifted ; output of the hysteresis switch 23 of the tracking oscillator is taken from the output of CMOS gate G9 to provide the desired polarity of the frequency-to-voltage transfer ratio.
The phase detector 15 may include an Exclusive-OR gate Gll. The low pass filter/averaging circuit 9 may contain an inverter and two active second order bypass low filters in series ~not shown) of a conventional design.
- lQ
:
, .
CM-76799 1~67S89 The reference Yoltage Rref may be maintained throughout the circuit at the threshold voltage of the CMOS gates and the voltage swings are symmetrical above and below the threshold voltage, as illustrated in Fig. 5~ This is accom-plished using negative eedback around various gates. This factor accounts for the use of various circuit components such as resistors R3, R8, R9, and gate Gl0 in the tracking oscillator and similar elements that may be used in the low pass filter and averaging circuit 17. In accordance with an aspect of the present invention, the tracking oscillator and the remaining circuit elements can be readily implemented by using conventional CMOS integrated circuits, capacitors and resistors and can be readily made in a hybrid circuit.
In summary, then, the present invention provides a tracking oscillator of a greatly simplified circuitry and novel utilization of such a tracking circuitry in combination with a limiter and a phase detector for providing a frequency-,.
to-voltage converter, The converter may be advantageously used as an FM discriminator, or frequency shift keying circuit as desired~ These features of the invention are shown implemented in the form of low cost CMOS integrated circuits. The overall frequency-to-voltage converter circuitry can be readily implemented essentially in two CMOS integrated circuits: one to include the limiter and tracking oscillator and the other to include the phase detector and the low pass filter and averaging circuit~ Each of these CMOS integrated circuits can be implemented with a single low cost digital ; integrated circuit.
Since C~OS integrated circuits are low cost elements, cost savings for tne overall circuitry is very significant.
. CM-76799 1~67589 Moreover, the use of the limited number of small circuit components renders the circuit more reliable. Also the present circuit is more suitable for implementation as a hybrid circuit than the prior art frequency-to-voltage converter circuits.
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Claims (3)
1. A tracking oscillator comprising:
an integrator and an hysteresis switch coupled in series, the integrator having a first and second input and an output, the second input for receiving a feedback from the output of the hysteresis switch, the integrator integrat-ing the incoming waves from the first input and decreasing its output linearly while the voltage at the second input thereof is at a first level voltage and the integrator integrating the incoming waves and increasing its output linearly while the voltage at the second input thereof is at a second level voltage, whereby the integrator provides a train of output wave changing between a low level threshold and a high level threshold voltage, the hysteresis switch changing its output from a low level voltage to a high level voltage. and vice versa as the output of the integrator traverses the low level and high level threshold and thereby producing a train of square wave output, and a feedback circuitry for applying the output of the hysteresis switch to the second input of the integrator for marking change in the direction of the integration of the input train of waves by the integrator.
an integrator and an hysteresis switch coupled in series, the integrator having a first and second input and an output, the second input for receiving a feedback from the output of the hysteresis switch, the integrator integrat-ing the incoming waves from the first input and decreasing its output linearly while the voltage at the second input thereof is at a first level voltage and the integrator integrating the incoming waves and increasing its output linearly while the voltage at the second input thereof is at a second level voltage, whereby the integrator provides a train of output wave changing between a low level threshold and a high level threshold voltage, the hysteresis switch changing its output from a low level voltage to a high level voltage. and vice versa as the output of the integrator traverses the low level and high level threshold and thereby producing a train of square wave output, and a feedback circuitry for applying the output of the hysteresis switch to the second input of the integrator for marking change in the direction of the integration of the input train of waves by the integrator.
2. A use of the tracking oscillator according to claim 1 in a frequency-to-voltage converter, the converter comprising:
a limiter and a phase detector and the tracking oscillator, the tracking oscillator providing a phase delay in the train of waves from the limiter and applying the phase delayed output to the phase detector, the phase detector comparing the output of the limiter and the phase delayed output of the tracking oscillator for providing an output train of waves wherein the width of the waves is proportional to the delay in phase introduced by the tracking oscillator, and a circuitry coupled to the output of the phase detector for converting the train of waves from the phase detector into a DC voltage proportional to the phase delay indicated by the pulse width of the output train of waves of the phase detector.
a limiter and a phase detector and the tracking oscillator, the tracking oscillator providing a phase delay in the train of waves from the limiter and applying the phase delayed output to the phase detector, the phase detector comparing the output of the limiter and the phase delayed output of the tracking oscillator for providing an output train of waves wherein the width of the waves is proportional to the delay in phase introduced by the tracking oscillator, and a circuitry coupled to the output of the phase detector for converting the train of waves from the phase detector into a DC voltage proportional to the phase delay indicated by the pulse width of the output train of waves of the phase detector.
3. The frequency-to-voltage converter according to claim 2, wherein the limiter, the tracking oscillator, the phase detector and the circuitry coupled to the output of the phase detector are selectively and in combination imple-mented in CMOS integrated circuits.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,140A CA1067589A (en) | 1977-03-16 | 1977-03-16 | Tracking oscillator and use of the same in a frequency to voltage converter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,140A CA1067589A (en) | 1977-03-16 | 1977-03-16 | Tracking oscillator and use of the same in a frequency to voltage converter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1067589A true CA1067589A (en) | 1979-12-04 |
Family
ID=4108177
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,140A Expired CA1067589A (en) | 1977-03-16 | 1977-03-16 | Tracking oscillator and use of the same in a frequency to voltage converter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1067589A (en) |
-
1977
- 1977-03-16 CA CA274,140A patent/CA1067589A/en not_active Expired
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