FR2492987A1 - Phase difference measuring circuit for same fundamental frequencies - mixes signal of multiple frequency of input to obtain two phase differing signals which are filtered to retain one component of each signal - Google Patents

Abstract

The device measures the phase difference between two harmonically related signals VR1 and VR1 and is partic. useful for frequencies higher than 1 MHz. A generator (1) produces a signal VO whose frequency is approximately equal to the fundamental, a multiple, or a submultiple of the frequency of one of the signals VR1 and VR2. This signal VO is mixed with both signals VR1 and VR2 in order to produce two signals V1 and V2 whose phase difference is equal to that between signals VR1 and VR2. The signals V1 and V2 are then filtered so that one component of each is retained. Finally the difference of phase between the two signals V1 and V2 is measured. The frequency of the signals V1 and V2 is stabilised and the signals V1 and V2 are amplified after being filtered.

Description

DEVICE FOR MEASURING THE PHASE BETWEEN TWO

  SAME FREQUENCY OR FREQUENCY SIGNALS

  MULTIPLES IN PARTICULAR OF SUPE FREQUENCIES

  RIEURES AT 1 M Hz The present invention relates to a device

  measurement of phase shift between two periodic signals, in particular

  especially at frequencies above 1 M Hz.

  A nonlimiting example is the measurement of the phase shift between two signals used for the sinusoidal light injection in which one of the signals constitutes a reference of sinusoidal shape delivered by the generator which ensures the

  modulation of the light while the other signed, supplied direct

  the photoreceptor, is most often

  low level and disturbed by the noise of the photoreceptor and

  times by undesirable tensions. Such measures require equipment having both good sensitivity,

  good detectivity and good selectivity.

  However, existing devices do not meet

  to such requirements. Indeed, the phasemeters are devices

  precise but weak sensitivity and poor detection

  vity and do not allow measurement at frequencies above 10 M1 Hz; vector voltmeters can work with fairly good sensitivity up to frequencies of around 1000 Il Hz but with poor noise immunity and above all

  with a lower precision which depends moreover on the relative level

/ to the windows /

  tif applied voltages /; synchronous detectors have

  tooth a great sensitivity and a strong detectivity but does not

  are precise only for frequencies lower than I M- Hz.

  The object of the present invention is to re-

  mediate these disadvantages and provide an accurate measurement device with good sensitivity and good detectivity

  in a frequency range from 1 to '100} Hz. It is clearly understood

  that this frequency range is indicated by way of nonlimiting example and that the device according to the invention could be applied to different frequencies, in particular higher frequencies,

  for example in the microwave domain.

  Another object of the invention is to provide a simple and precise device despite the fact that the signal whose phase shift is to be measured with respect to a reference signal

  either low level and disturbed by undesirable voltages.

  The device according to the present invention finds its essential characteristic in the fact that it is provided with: means for generating a periodic signal whose frequency is of the same order of magnitude as the frequency of one or both signals VR1 and VR2 or of the same order of a multiple or submultiple of these frequencies, - means of mixing this signal with the two signals VR1 and VR2 in order to obtain two signals V1 and V2

  periodicals whose phase difference is equal to the difference

  phase rence between the signals VRt and VR2, - means for filtering the signals VI and V2 in order to preserve one of the components of each of the signals, - means for measuring the difference of

phase between signals V1 and V2.

  Another characteristic of the device according to the invention resides in the fact that it comprises means for amplifying the signals V1 and V2 before measuring their phase shift. Amplification is done at low frequency

  is easier. This amplification can also be different

referred to according to the signals.

  Another feature of the device

  according to the invention is that it is provided with stabllisa-

  in frequency of the signals V1 and V2 which allows a feeling

  optimal measurement sensitivity despite selective amplification

  used. This stabilization is ensured by means of a bou-

  phase locked key comprising a reference oscillator

  control, a bandpass amplifier, a comparison

  3- phase detector and a low-pass circuit.

  In the accompanying drawings is shown in

  non-limiting title an embodiment of the object of il.n

  vention; in these drawings: - Figure 1 is a block diagram showing the operating principle of the device according to the invention, - Figure 2 is a block diagram of the device according to the invention with frequency stabilization means,

24929X7

  - Figure 3 is the diagram of an oscillator

  voltage-controlled, - Figure 4 is the diagram of a mixer, - Figure 5 is the diagram of a selective amplifier, - Figure 6 is the diagram of the stabilization oscillator,

  - Figure 7 is the diagram of the low-pass circuit.

  gae In Figure 1, a frequency oscillator 1

  glable delivers a sinusoidal signal V0, of frequency fo and

  phase 'o. This signal is mixed on the one hand with the sinu-

  reference solenoid VR1 of frequency fR and of phase4 1 by the

  through a mixer 2 and on the other hand with the signal if-

  nusoidal disturbed VR2 of frequency fR and phasel2 by the

  middle of mixer 3. At the output of mixer 2, a sinusoidal signal Vi is obtained after filtering and amplification in the

  circuits 5 and 6, having a frequency F = fO - fR and a pha-

  is 0 - 1 + 4 '. At the outlet of the mixer 3, a

  sinusoidal V2 after filtering and amplification in the circuits

  29 cooked 5 and 7, having a frequency F = fO - fR and a phase

CQ - I +

  By appropriately choosing the frequency f0, one can obtain a frequency F lying in the low frequency range and use a phasemeter 8 to measure the phase difference between the signals V2 and VI which is equal to the difference

  phase between signals VR2 and VR1.

  One of the advantages of this system is that the input voltages VR1 and VR2 can be lower

  amplitude than that required by the phasemeters because the amplification

  tion at low frequency F is easier than that at broad frequency

  of at frequencies fR. In addition, optimal sensitivity can be obtained using selective amplification, taking care, however, to stabilize the frequency fO - fR = F. This result can be achieved using a phase locked loop in which the frequency difference fO - fR is slaved to a pilot oscillator of stable frequency F. It is thus, FIG. 2 that a phase comparator 11 receives the signal of frequency F from a pilot oscillator 9 and

  that, of frequency fO - fR of the input mixer 2 after step-

  wise in a bandpass amplifier 10. The voltage obtained at the output of this comparator is subjected to a low-pass circuit 12. The voltage

  obtained at the output of this circuit constitutes the con-

oscillator command 1.

  This oscillator, as shown in FIG. 3, comprises an oscillating circuit LC 13 with variable capacitor 14, the operation of which makes it possible to place the loop in locking mode. The maintenance of this is ensured by the output signal of the low-pass circuit 12 controlling the varactors 15 and 16. The oscillator also includes a common collector stage 17 and two impedance matching circuits 18 and 19 including the outputs are respectively connected to mixer 2 and

in the mixer 3.

  In fact, given the wide range of working frequencies, a single oscillator could not be satisfactory. Indeed, the ratio fR must not be too F.

  important if you want to avoid too high phase noise.

  We will therefore use at least two oscillators of this type per decade. Mixers 2 and 3 being identical, we will limit ourselves to describing only one of them. Thus, Figure 4 we see a balanced mixer Schottky diodes whose advantage is to have a lower factor of

  noise than active component mixers.

  Given the particularly high values that the frequencies fR and fO can take, it is necessary to adapt the impedance of the input gates fo and fR

  hence the need for circuits 18 and 19 at the exit of the oscil-

  lators 1. The signal at the output of the mixers must be

  very before use in order to keep only the frequency term fO - fR and in particular to eliminate the frequency term

  fo + fR. The low-pass filter used consists of the resistance

  source of the mixer and a capacitor placed at the terminals

  from the output of gate F. The signals, now filtered, must be amplified. For this we will use selective amplifiers as described in the diagram in Figure 5. Given the risk of saturation by undesirable voltages,

  we have chosen a field effect transistor 21 whose fac-

  this noise, although more important than that of a bipolar transistor, remains within satisfactory limits. The components of the tuning circuit 22 are identical to those used in the reference oscillator 9 in order to limit the consequences

frequency shift.

  The disturbed signal being generally of very low amplitude, it seemed desirable to add a bandpass amplifier following the selective amplifier 7 on the path of the disturbed signal. This amplifier is set so that

  the cut-off frequencies are close to F and 3F.

2 2

  esaataex As we saw in the preamble, it

  it is advantageous to stabilize the frequency signals in frequency

  ce fO - fR = F. We use a locking loop for this.

  phase comprising a reference oscillator 9, an amplifier

  10 bandpass cator, a phase comparator 11, and a lowpass circuit 12 to which a divider or

a frequency multiplier.

  This reference oscillator is described fi-

  gure 6. It comprises three stages: the oscillator 23 proper, a selective amplifier stage 24 and an impedance matching stage 25. As can be seen, it is an oscillator

  with electronic coupling between base and transmitter. The ac circuit

  / selective 24 / cord 26 of the amplifit-e U7 stage - identical to that of the 22

  selective amplifiers 6 and 7. This oscillator delivers a

  frequency of F to a phase comparator 11 which is not

  be a mixer with the same structure as that of the mixers 2_ mentioned previously. This phase comparator receives a signal from the mixer on the reference channel via a

  bandpass amplifier 10 comprising two amplification stages

  voltage sensors and a common collector stage, ndepedance adapter. At the output of the phase comparator, the signal is delivered to the voltage-controlled oscillators 1 through a low-pass circuit which we will describe in relation to the

figure 7.

  The purpose of this circuit is to eliminate the 2F frequency components delivered by the comparator, rais

  also to make the phase correction necessary for the function

  stable operation of the locking speed loop. This is

the role of the network 27.

  The Vo component of the signal delivered by

  oscillator 1 is obtained by applying, on the inverting input

  threshold of an operational amplifier 28, a negative voltage of adjustable amplitude. So that Vo is stable and does not contain any undesirable component, the voltage -V already filtered and stabilized is applied to a stabilizer circuit 29 with a diode.

  zener 30 and filter capacitor 31.

  All DC supply voltages are filtered and stabilized before being applied

  to the various amplifier circuits. and oscillators.

  Of course, the invention is not limited

  as described above, but includes all

  your variants. For example, the device can be made

  so as to benefit from automatic operation. The brother

  quence FR of the signal VR1 or VR2 is measured by a frequency m

  be digital which directly selects the range of iosci! 1a-

  tion 1 necessary for the proper functioning of the device. A conver-

  Digital / Analog weaver giving continuous tension or

  slowly variable, depending on the frequency FR, allows posi-

  operate oscillator 1 so that signals V1 and V2 pre-

  feel a frequency located in the capture range of the phase locked loop {constituted by the means 1, 2,

9, 10, 11 and 12).

Claims (9)

  1 / - Device for measuring phase shift between   two signals VR1 and VR2 of the same frequency or of multiple frequencies   multiple, in particular of frequency higher than 1 M Hz, charac-   verified by: - means for generating (1) a periodic signal whose frequency is of the same hiker order as the frequency of one or both signals VR1 and VR27on the same order of a multiple or submultiple of these frequencies, - means for mixing (2, 3) this signal with the two signals VR1 and VR2 in order to obtain two signals (VI) and   (V2) periodicals whose phase difference is equal to the diff-   phase ference between the signals VR1 and VR2, - filtering means (4,5) of the signals (vl) and (V2) in order to preserve one of the components of each of the signals, - measuring means (8) of the difference   phase between signals (Vi) and (V2).   2 / - Device according to claim 1, characterized in that it comprises means (9, 10, 11, 12) for stabilizing the frequency of the signals (V1) and (V2) using a loop phase lock controlled by an oscillator reference (9).   3 / - Device according to claim 2,   characterized in that the means (9, 10, 11, 12) of staDilisa-   tion of]. the frequency of the signals (V1) and (V2) include   the oscillator] (9), a bandpass amplifier (10), a comp   phase generator (11) and a low-pass circuit (12).   4 / - Device according to claim 1, characterized in that the means for generating (1) the sinusoidal signal comprise at least one oscillator controlled by a electrical or mechanical quantity.   / - Device according to claim 4, characterized in that the generation means (1) comprise   at least two oscillators per decade.   6 / - Device according to claim 5 characterized in that the oscillators comprise an oscillating circuit (13) with variable capacitors (14) for cbterter un   locking system and varacto.rs (15, 16) for main-   maintain this regime, one stage with a common collector (17) and two states--   impedance adapters (18,19).   7 / - Device according to one of the claims   1, 2, 3, 4, 5, ou.6, characterized in that the means for mixing (2, 3) the sinusoidal signal with each of the two signals   VR1 and VR2 are Schottky diode mixers.   8 / - Device according to one of the claims   1, 2, 3, 4, 5, 6 or 7, characterized in that the filtering mcyens (4, 5) of the signals (V1) and (V2) are low-pass filters constituted by the source resistance of the mixers   (2, 3) and by capacitors placed between the output terminals tie of these mixers.   9 / - Device according to one of the claims   1, 2, 3, 4, 5, 6, 7 or 8, characterized in that it comprises   amplification means <6, 7) of the signals V1 and V2.   / - Device according to claim 9,   characterized in that the amplification means (6, 7) of the si-   gnaux (V1) and (V2) are constituted, for the signal (V1), by a selective amplifier (6) with field effect transistors and,   for the signal (V2), by a selective amplifier (7)   field effect sistors followed by at least one bandpass amplifier.   11 / - Device according to one of the claims   1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, characterized in that the filtering means (4, 5) are adapted to preserve the low frequency component of each of the signals (V1) and (V2) and in that the measuring means (8) consist of a   low frequency phasemeter or a synchronous detector.