JPH0448021B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a signal source that generates a signal with a predetermined temporally variable frequency, and a The present invention relates to a system comprising a signal utilization device for executing a process.

PRIOR ART In one example of such a system, the signal source comprises a voltage-controlled oscillator, which is responsive to a time-variable input signal S ₀ (t) and is approximately directly proportional to the input signal. An output signal having a predetermined time-varying frequency is generated. The signal utilization device consists of a laser scanner and uses an acousto-optic modulator to deflect the laser beam by an angle proportional to the frequency of the input signal. As another example, the signal-utilizing device comprises an interrogator-answer system that transmits an interrogation signal with frequencies that are sloped generally upwardly and/or downwardly within a predetermined frequency range.

In systems such as those described above that respond to monotonically rising or falling frequencies, nonlinearity of frequency with respect to time or with respect to another signal or voltage introduces errors into the signal utilization device.
Previous attempts to compensate for nonlinearity have primarily been directed to methods and means of linearizing the time or voltage versus frequency function itself. Thus, for example, a feedback loop was provided between the output of the signal source and its control input in order to correct for output non-linearities.

(Object of the invention) An object of the invention is to provide a device for compensating for nonlinearity in the time behavior of the frequency f(t) of the first signal.

Arrangements of the Invention The above and other objects, which will become apparent from the following description, are provided by an apparatus which is connected to receive a first signal and which transmits the first signal with a predetermined signal delay (T ₁ ).
a delay element that generates a second signal delayed by the first
and a signal mixer that mixes both the second and second signals to generate a third signal; and a device that responds to the third signal and generates a sampling signal having a frequency corresponding to the frequency of the third signal. It is achieved by doing so. For reasons detailed later, the above sampling signal has a frequency of the first signal that is a predetermined amount △f (however, △f = 1/T ₁ or a perfect fraction thereof, that is, an integer multiple).
Limit the moment when only that changes.

Further in accordance with the invention, the sampling signal described above is provided to a signal utilization device which is responsive to a change in the first signal frequency by a predetermined amount defined by the sampling signal.

In one preferred embodiment of the invention, the delay element provides a constant signal delay T ₁ . In another embodiment,
The delay T ₁ is a known function of the frequency f(t) of the first signal. In the latter case, where the delay T ₁ is a function of frequency,
The predetermined amount of frequency change between the instants of time defined by the sampling signal is also frequency dependent.

For a complete understanding of the invention, reference is made to the following detailed description of the preferred embodiments of the invention and the accompanying drawings.

(Embodiments of the Invention) The present invention will be described below with reference to FIGS. 1 to 12 of the accompanying drawings. Identical elements in the figures are designated by the same reference numerals.

FIG. 1 shows the entire system according to the invention for providing a signal S ₁ with a monotonically temporally variable frequency f ₁ and a sampling signal S ₅ with a specific sampling frequency f ₅ to a signal utilization device 10. ing.
The signal utilization device may be any device that responds to the signal S ₁ and performs a certain procedure or operation depending on the frequency f ₁ . Two specific examples of this type of signal utilization device will be described later with reference to FIGS. 5-12.

For purposes of general description, assume that the signal-utilizing device 10 is responsive to a time-varying frequency f ₁ and that deviations between the actual and desired values of this frequency result in unacceptable errors in the operation of the signal-utilizing device. Suffice it to say here.

Signal S ₁ is generated by any suitable signal source 12. This signal source can for example consist of a voltage controlled oscillator (VCO) which generates an output signal S ₁ proportional to the input voltage S ₀ and of frequency f ₁ . That is: f ₁ (t)=KS ₀ (t)+k where K and k are constants.

As an example, the input voltage S ₀ consists of a sawtooth signal that slopes linearly upward repeatedly from a minimum value to a maximum value. This input signal varies from the initial value f _nio to the maximum value
This results in an output signal S ₁ with a frequency f ₁ that slopes approximately linearly upward to f _nax . In this configuration the frequency f ₁
Exact linear upward slope of (df ₁ /dt = constant)
There are two causes for the deviation from: 1. The input voltage S ₀ is not exactly linear with respect to time (df ₁ /dt = constant); 2. The frequency f ₁ is not exactly linear with respect to the input signal S ₀ exactly straight
f ₁ = KS ₀ + k).

In most cases, this nonlinearity of signal f ₁ does not adversely affect the operation of signal utilization device 10 . But in some applications, that nonlinearity is not tolerated and f ₁
It is necessary to correct or compensate for deviations from the desired value.

Of course, to improve linearity, the voltage source S ₀
Some corrective measures can be taken, such as improving the quality of the signal source 12 (such as a slope generator), and also improving the linearity between frequency f ₁ and signal S ₀ .

Additionally, it is well known to provide a phase lock loop between the output and input of signal source 12 to maintain the linearity of the signal source. This solution uses the initial voltage signal
It has the disadvantage of increasing system complexity without compensating for the nonlinearity of S ₀ .

According to the invention, the system comprises a separate device for generating and supplying to the signal utilization device 10 a sampling signal S ₅ defining the time instant at which the frequency f ₁ of the first signal S ₁ has changed by a predetermined amount.

According to the invention, the sampling signal S ₅ is generated as follows: An initial signal S ₁ of frequency f ₁ is directly and a delay period T ₁
is fed indirectly to the four-quadrant mixer 16 via a delay element 18 having a . That is, the output signal S ₂ of the delay element 18 with frequency f ₂ is also applied to the mixer 16 .

In this particular embodiment, signal S ₁ is applied directly to mixer 16 and delay element 18, but signal S ₁
It will be appreciated that a further signal may be passed through a frequency multiplier, divider, etc. and applied to mixer 16 and delay element 18. The key point in the present invention is that the frequency of the signal applied to the mixer and the delay element is the same as or derived from the frequency _f1 ,
It is related to and synchronized with that.

Mixer 16 produces an output signal S ₃ with a frequency f ₃ equal to the sum and difference of frequencies f ₁ and f ₂ . this signal
S ₃ is applied to a filter such as low-pass filter 20, resulting in a signal S ₄ containing only the difference frequency included in signal S ₃
occurs. This signal S ₄ is then applied to a sampling device 22 which produces a sampling signal S ₅ having a sampling frequency f ₅ .

Sampling device 22 can be configured as shown in FIG. The device consists of one or more frequency doublers 24 such that the sampling frequency f ₅ is a multiple of the frequency f ₄ . Frequency multiplier (doubler) 2
The output of 4 is sent to a zero-crossing detector, producing a sampling pulse for each zero-crossing that goes positive or negative.

Next, the operation of the device 14 shown in FIG. 1 will be explained with reference to the diagrams in FIGS. 3 and 4. These diagrams show the frequency f ₁ as a function of time.
As is clear from the figure, frequency f ₁ is the minimum frequency
It slopes upward from f _nio to the maximum frequency f _nax and then drops sharply again to the minimum frequency f _nio . frequency
f ₁ is a linear function of time between two limits;
Preferably, df ₁ /dt=constant. but,
Providing a signal source with a precisely linear output frequency is extremely expensive. 3 and 4 show the nonlinearity at frequency f ₁ in an exaggerated manner for ease of understanding.

In FIG. 3, the frequency f ₂ of the signal S ₂ is also indicated by a dotted line. This frequency is equal to the frequency f ₁ , but the period T ₁
Only has been delayed. As is clear from the figure,
The frequency difference between f ₁ and f ₂ at a given time instant (eg t ₀ ), ie the frequency of the signal S ₄ appearing at the output of the low-pass filter 20, is f ₄ . Signal S ₂
is simply the delayed signal S ₁ , so the time t ₀
The slope of the frequency curve f ₁ at is approximately given by: df ₁ /dt=f ₄ /T _1.The slope of the frequency curve f ₁ is then defined as: df ₁ /dt= Δf/TΔ _f where Δf is the change in frequency f ₁ during the period TΔ _f .

Now, the period T△ _f is T _f4 (period of signal S ₄ and frequency f ₄ )
f ₄ /T ₁ = △f/T _f4 Since f ₄ = 1/T _f4 , Δf = 1/T ₁ = constant Therefore, the signal S ₄ (frequency f ₄ and period T ₄ ), the frequency f ₁ changes by a fixed amount Δf. That is, a sampling signal with a frequency of f ₅ =Mf ₄ , where M is an integer, defines each instant at which the frequency of signal S ₁ changes by a predetermined amount.

FIG. 4 shows in an exaggerated manner how the sampling pulses appear at successive time instants t ₁ , t ₂ . . . _{t t} giving an equal change Δf of frequency f ₁ .
The magnitude of the frequency change Δf is determined by T ₁ and the integer M.

FIG. 5 shows a system for scanning a laser beam 40 across a screen or other surface 42. FIG. Scanning is accomplished by an acousto-optic modulator 44.

A voltage controlled oscillator 46 provides a signal at frequency f to the modulator plates. The deflection angle θ of the beam 4 is
It is directly proportional to its frequency.

It will be appreciated that a linear sweep of frequency f results in a constant scanning speed across the screen surface 42. However, unavoidable nonlinearities distort the images produced by the scanner.

In accordance with the present invention, a sampling signal is applied to a Q-switch 48 which modulates the beam to define the increments of time that the beam is scanned along screen 42 by equal spatial increments ΔS. These spatial increments can be made as small as desired by appropriate selection of the delay period T ₁ of the device 50 for generating the sampling signal and the frequency multiplier M.

6 to 12 show an example in which the present invention is applied to a calling machine-responding machine system using a surface acoustic wave transponder. A general version of this type of system is disclosed in US Pat. No. 3,706,094 to Cole and Vaughn.

The oscillator/transmitter and decoder system shown in FIG. 6 includes a ramp generator 90 that provides a sawtooth waveform to a voltage controlled oscillator (VCO) 92. The VCO produces an output signal with a frequency f that repeatedly ramps upward linearly from a frequency of 905 MHz to a frequency of 925 Hz. This output signal is amplified by an RF amplifier 94 and applied to a transmit/receive switch 96. Switch 96 directs the signal to power amplifier 98 or decode mixer 100 on the oscillator side. Switch 96 is controlled by a 100 KHz square wave signal generated from clock 102.
The output signal S ₁ from amplifier 98 is routed to an external circulator or transmit/receive (TR) switch 104.
and is transmitted as electromagnetic radiation from the antenna 106.

A block diagram of a transponder associated with the system of FIG. 6 is shown in FIG. The transponder receives the signal S ₁ on antenna 107 and transmits it for the indicated delay period.
To a series of delay elements 109 having T ₀ , ΔT.
Part of the signal after passing through each successive delay element
I ₀ , I ₁ , I _{2 . .} . I _N are taken out and provided to summation element 111. A total signal that is the sum of each intermediate signal I ₀ ...I _N
S ₂ is returned to antenna 107 and transmitted to antenna 106 in the system of FIG.

The response signal S ₂ from the responder is received by antenna 106 and sent via circulator or TR switch 104 to receiver amplifier 108 . The output S ₄ of the amplifier 108 is heterodyne mixed with the signal S ₃ intermittently applied from the switch 96 in the mixer 100 .

The output S ₅ of mixer 100 includes the sum and difference frequencies of both signals S ₃ and S ₄ . This output is applied to a bandpass filter 110 having a passband of 1 to 3KHz. The output of the filter passes through an antialiasing (to prevent frequency folding) filter 112 to a sample/hold circuit 114 .

A sample/hold circuit provides each sample to an analog-to-digital (A/D) converter 116. The A/D converter provides the sampled digital values to a processor 118 which analyzes the frequencies contained in the signal using a Fourier transform. The sample/hold circuit 114 and the A/D converter 116 are strobed by a sampling signal generated by a device 119 according to the invention. As mentioned above, this sampling signal compensates for the non-linearity with respect to time of the monotonically increasing frequency f of the VCO output signal.

Device 119 inputs the signal generated by VCO 92 via separation amplifier 121 . The signal is further
It is passed through a delay element 120 with a constant signal delay T _s . Both the delayed and undelayed signals are applied to mixer 122, which produces a signal S ₇ containing the sum and difference frequencies. The signal S ₇ is applied to a low pass filter 124 that passes only the portion containing the signal's intermediate frequency. The output of the low pass filter is fed to a zero crossing detector 126, which generates one pulse for each positive (or negative) going zero crossing. These pulses are used to strobe sample/hold device 114 and A/D converter 116.

10-12 illustrate the operation of the circuit of FIG. 6. Figure 10 shows 100KHz from clock 102.
Output: Figure 11 shows the frequency sweep of the signal generated by the VCO 92, and Figure 12 shows the frequency of the transmitted signal S ₁ (solid line 128) and the frequency of the signal S ₂ received from the transponder (dotted line 130), respectively. ing. As can be seen, signal 130 is received during the transmission interval of signal 128. These intervals are chosen to be approximately equal to the round trip delay time between issuing a signal to the transponder and receiving a response from the transponder. As shown by multiple dotted lines in the figure, responses from transponders have different delay times (T ₀ , T ₀ +△T, T ₀ +2△
The result is a combined (i.e., summed) intermediate signal with T _, .

8 and 9 show an embodiment of a transponder implementing the block diagram of FIG. The transponder operates to convert the received signal S ₁ into an acoustic wave and to convert the acoustic energy back into an electrical signal S ₂ for transmission via the dipole antenna 56 .
That is, the signal transducing element of the transponder has a substrate 58 made of a piezoelectric material, such as a sodium niobate (LiNbo ₃ ) crystal. A metal layer, such as aluminum, forming a pattern as shown in FIG. 9 is deposited on the surface of the substrate. This pattern consists, for example, of two bus bars 60, 62 connected to a dipole antenna 56, an "launch" transducer 64, and a plurality of "tap" transducers 66. In this way, the bus bar 60,
62 is generated by the starting transducer;
A travel path 68 is defined for the acoustic waves that propagate in a substantially straight line and reach each tap transducer in sequence. Tap transducers reconvert the acoustic waves into electrical energy, which is collected and summed into busbars 60, 62. Then the total electrical energy is transferred to the dipole antenna 5
6 is converted into electromagnetic radiation and transmitted as signal S ₂ .

The tap transducers 56 are spaced equally apart along the acoustic wave path 68 as shown in FIG. A corresponding information code is given. These delay pads, shown in detail in FIG.
and the same material as the transducers 64 and 66,
Preferably, it is coated. Each delay pad is
The propagation of an acoustic wave from one tap transducer 66 to the next transducer is 1/1 compared to an acoustic wave that is not delayed at the operating frequency (approximately 915 MHz).
It has enough width to delay 4 periods or 90 degrees.
By placing three delay pads between successive tap transducers, the phase φ of the acoustic wave received by tap transducer 66B can be controlled to provide the following four types of phases: : 1 No pad between tap transducer 66A, 66B = -90°; 2 1 pad between tap transducer 66A, 66B = 0°; 3 Pad 2 between tap transducer 66A, 66B 90°; and 3 pads between the 4 tap transducers 66A and 66B = 180°.

Referring to FIG. 7, the phase information φ ₀ (first
φ ₁ , _{φ 2} . It is supplied to a combiner (adder) consisting of 60 and 62. antenna 56
The above phase information transmitted as signal S ₂ from the transponder includes the information code of the transponder.

There has thus been illustrated and described a novel apparatus for compensating for nonlinearities in frequency modulated signals that satisfies all objects and advantages of the present invention. Many changes, modifications, variations and other uses and applications of the present invention will be apparent to those skilled in the art from the specification and accompanying drawings which disclose the preferred embodiments. All such changes, modifications, variations and other uses and applications that do not depart from the spirit and scope of the invention are intended to be included in the invention, which is limited only by the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device according to the invention for compensating nonlinearities in a frequency modulated signal. Second
1. The figure is a block diagram of detailed elements included in the sampling element in the apparatus of FIG. 3 and 4 are frequency versus time diagrams illustrating the operation of the apparatus of FIG. 1; FIG. 5 is a block diagram illustrating the use of the present invention in combination with a laser beam scanner. FIG. 6 is a block diagram illustrating the use of the present invention in conjunction with an interrogator-answer system. FIG. 7 is a block diagram of a passive transponder used in the system of FIG. FIG. 8 is a specific diagram showing a preferred embodiment of the answering machine shown in FIG. 7. FIG. 9 is a detailed diagram showing a part of the transponder shown in FIG. 8.
10 and 11 are voltage and frequency timing diagrams showing the operation of the system of FIG. 6, respectively. FIG. 12 is a frequency versus time diagram further illustrating the operation of the system of FIG. 10... Signal utilization means, 12... Signal source means,
14,50,119...device of the present invention, 16,1
22...Mixing means, 18,109...Delay element,
22...Sampling signal generating means, 40...Laser beam, 44...Beam deflector, 48...Beam intensity modulator, 90-106 (excluding 100)...
... Fourth signal generation means, 100 ... Sixth signal generation and mixing means, 104 ... Transmission/reception switch, 56 -
70,107-111...Response machine means (64,6
6,109...Signal converting means, 70...Signal adjusting means, 60,62,111...Signal combining means),
114-118...Signal processing means.

Claims (1)

[Claims] 1. (a) Signal source means for generating a first signal having a temporally variable frequency f(t) having a monotonically varying time differential coefficient (df/dt), and ( b) In a system comprising signal utilization means responsive to the first signal and executing a desired process depending on the frequency f(t) of the first signal, (a) receiving the first signal as an input signal; (b) mixing said first and _second signals to produce a third signal; and (c) means for generating a sampling signal having a frequency corresponding to the frequency of the third signal in response to the third signal, the sampling time of the sampling signal being a predetermined amount Δf (Δf=1/ _T1 or an integer multiple thereof), and the signal utilization means responds to the sampling signal to perform the desired process when the frequency f(t) changes by the predetermined amount Δf. A device for compensating for the non-linearity of the differential coefficient (df/dt), comprising: taking necessary treatment steps. 2. A system for calling a passive transponder in which the signal utilization means transmits coded information, the system comprising: (a) a fourth frequency having a second frequency corresponding to the first frequency f(t); means for transmitting a signal, the second frequency continuously having a plurality of frequency values within a predetermined frequency range; (b) receiving the fourth signal and, in response, transmitting a fifth signal;
remote passive transponder means for emitting a signal, the transponder means further comprising signal conversion means connected to receive a fourth signal as an input to produce a fifth signal as an output; (a) a plurality of signal conditioning means connected to receive a fourth signal, each signal conditioning means providing an intermediate signal with a known delay and a known amplitude change to the fourth signal; b) signal combining means connected to all of said signal conditioning means and for combining said intermediate signals to produce said fifth signal; (c) means for receiving a fifth signal from the transponder means; (d) configured to receive the fourth signal and the fifth signal; means for mixing the signals to generate a sixth signal; and (e) responding to the sixth signal and detecting at least a portion of the frequencies contained in the sixth signal, corresponding to transponder means. 2. The apparatus according to claim 1, further comprising signal processing means for determining said information code. 3. The signal utilization means comprises a laser beam scanner, the scanner comprising: (a) a laser producing a laser beam; and (b) disposed in the optical path of the laser beam and configured to scan the beam in response to at least one input signal. (c) a laser beam modulator for controlling intensity; (c) disposed in the optical path of the laser beam;
a beam deflector connected to input the signal and deflecting the laser beam in proportion to the frequency f(t) of the first signal; 2. The apparatus of claim 1, wherein: is applied as an input signal to a beam modulator.