JP3099979B2 - Method and apparatus for measuring additional phase noise - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for testing two-port devices. In particular, the present invention relates to measurement of additional phase noise of a circuit having different frequencies between an input and an output.

[0002] In this specification, the term "two-port device" refers to an electric circuit or an electronic circuit such as an amplifier, a frequency divider, a mixer, a multiplier, a phase-locked loop oscillator, etc., which can obtain one output with respect to one input. Say.

[0003]

2. Description of the Related Art FIGS. 4 and 5 show a conventional method for measuring the additional phase noise. FIG. 4 shows a case where the input and output frequencies are the same, and FIG. 5 shows a case where both frequencies are different.

When measuring a circuit having the same frequency between the input and the output of an amplifier or the like, an output signal of a signal source 1 is split by a power splitter 2 and one of the output signals is split into a circuit under test 1
00 and the other is input to the 90 ° phase shifter 3. Further, the output of the circuit under test 100 and the output of the 90 ° phase shifter 3 are input to a phase detector 4, the output of which is passed through a low-pass filter 5, and a power spectrum is observed by a spectrum analyzer 6.

In the case of a circuit having a different frequency between the input and the output, such as a frequency divider, a mixer, a multiplier, and a phase-locked loop oscillator, an equivalent circuit is inserted in the stage preceding the 90 ° phase shifter 3. That is, one of the signals split by the power splitter 2 is input to the circuit under test 100-1, and the other is passed through the circuit under test 100-2 equivalent to the circuit under test 100-1, and the 90 ° phase shifter 3 is turned on. To enter. The output of the circuit under test 100-1 and the output of the 90 ° phase shifter 3 are input to the phase detector 4 and supplied to the spectrum analyzer 6 via the low-pass filter 5.

Here, a case where the input and output frequencies are the same will be described. The output signal A (t) of the signal source 1 is expressed as A (t) = A sin (ωt + φ _{REF, n} (t)) (1) A and ω are the amplitude and angular frequency, and φ _{REF, n} (t) is the phase noise of the signal, that is, the jitter. Circuit under test 1
Since 00 has the same frequency for the input and the output, the output signal is as follows: B (t) = Bsin (ωt + φREF _{, n} (t) + φDUT _{, n} (t)) (2) B is the amplitude, and φ _{DUT, n} (t) is the phase noise added in the circuit under test 100. As for the output signal of the 90 ° phase shifter 3, ignoring the phase noise added there, C (t) = C sin (ωt + φREF _{, n} (t) + 90 °) = Ccos (ωt + φREF _{, n} (t)) (3) The phase detector 4 is a multiplier whose output is: D (t) = B sin (ωt + φREF _{, n} (t) + φDUT _{, n} (t)) × Ccos (ωt + φREF _{, n} (t)) = (BC / 2) sin (2ωt + 2φREF _{, n} (t) + _{φDUT, n} (t)) + (BC / 2) sin ( _{φDUT, n} (t)) (4) The first term of this equation is the high frequency component, which is removed by the low pass filter 5. Further, since φ _{DUT, n} (t) is minute, D (t) ≒ (BC / 2) φ _{DUT, n} (t) (5) By inputting this voltage to the spectrum analyzer 6, a power spectrum of Sφ (f _m ) = [φ _{DUT, n} (f _m )] ² (6) is obtained. Where Φ
_{DUT, n} (f _m ) is a Fourier expansion of φ _{DUT, n} (t). That is, the phase noise of the signal source 1 is canceled and the circuit under test 100
Can measure only the phase noise.

If the input and output have different frequencies, the output signal of the circuit under test 100-1 is: E (t) = Esin (ω't + φ'REF _{, n} (t) + φDUT1 _{, n} (t)) ... (7) However, it is assumed that the output signal of the signal source 1 is represented by the expression (1). In the equation (7), E is amplitude, ω 'is the output angular frequency of the circuit under test 100-1, and φ' _{REF, n} (t) is the phase of the signal source 1 output via the circuit under test 100-1. The noise φ _{DUT1, n} (t) is the phase noise added in the circuit under test 100-1. Also, ignoring the phase shift noise added by the 90 ° phase shifter 3, the signal passing through the circuit under test 100-2 and the 90 ° phase shifter 3 is given by F (t) = Fsin (ω′t + φ ′) _{REF, n} (t) + φDUT2 _{, n} (t) + 90 °) = Fcos (ω′t + φ′REF _{, n} (t) + φDUT2 _{, n} (t)) (8) Here, F is the amplitude, and φ _{DUT2, n} (t) is the phase shift noise added by the circuit under measurement 100-2. Therefore,
The signal that has passed through the phase detector 4 and the low-pass filter 5 is as follows: G (t) = (EF / 2) [φ _{DUT1, n} (t) −φ _{DUT2, n} (t)] (9) Become. Since the noises generated in the circuits under test 100-1 and 100-2 have no correlation with each other, the power spectrum of the expression (9) is observed as a sum of the individual components, and Sφ (f _m ) = [Φ _{DUT1, n} (f _m ) ² + [Φ _{DUT2, n} (f _m )] ² (10) Φ _{DUT1, n} (f _m ) and Φ _{DUT2, n} (f _m ) are φ
_This is a Fourier expansion of _{DUT1, n} (t) and _{φDUT2, n} (t).

That is, the phase noise of the signal source 1 is canceled and only the noise of the circuits under test 100-1 and 100-2 can be measured. However, since these two circuits generate noise independently, the noise measurement results The value obtained by multiplying by す な わ ち, that is, the value obtained by subtracting 3 dB in dB display, is the noise per circuit to be measured.

[0009]

However, if there is a phase shift noise φ _{90, n} (t) added by the 90 ° phase shifter, the observed power spectrum is Sφ (f _m ) = [ Φ _{DUT1, n} (f _m )] ² + [φ _{DUT2, n} (f _m )] ² + [φ _{90, n} (f _m )] (11) Φ _{90, n} (f _m ) is a Fourier expansion of φ _{90, n} (t).

That is, in the conventional method of measuring the additional phase noise, the noise generated by the measuring system cannot be sufficiently separated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to provide an additional phase noise measuring method and an apparatus therefor capable of sufficiently separating noise generated by a measuring system.

[0012]

According to the additional phase noise measuring method of the present invention, a signal for measurement is passed through a circuit to be measured.
The passed signal is branched into two, and one of the signals is divided into 9
After passing through a 0 ° phase shifter, the other signal is multiplied, the phase noise of the measurement system is obtained from the multiplication result, and the phase noise of the measurement system is subtracted from the value measured by the conventional method. I do.

An apparatus for carrying out the method comprises a signal source, a power splitter for splitting the output of the signal source into two signal paths, and a 90 ° shifter disposed at one output of the two signal paths. A phase detector, a phase detector for multiplying the two signals passing through the two signal paths, an observation means for observing an output spectrum of the phase detector, and a connection for connecting a circuit under test to each of the two signal paths. And a connection switching means for short-circuiting the connection means to disconnect the circuit to be measured from the two signal paths and connecting one of the circuits to be measured between the signal source and the power splitter. It is characterized by.

[0014]

If the noise of the measuring system is measured without connecting the circuit to be measured, it can be distinguished from the noise due to the circuit to be measured. However, when the frequency of the input and output of the circuit under test is different, the frequency at the subsequent stage differs between when the circuit under test is connected and when it is not connected, and the measurement system cannot be measured correctly. Therefore, a circuit to be measured is inserted between the signal source and the power splitter, and the noise generated by the measurement system is measured by canceling out the additional noise of the signal source and the circuit to be measured. This noise is subtracted from the value obtained by the conventional additional phase noise measurement method. As a result, noise generated by the measurement system can be sufficiently separated, and accurate additional phase noise can be measured.

[0015]

FIG. 1 is a block diagram showing a first embodiment of an additional phase noise measuring method.

First, as shown in FIG.
From the signal to be measured is split into two by the power splitter 2, and one of the signals is split into the first circuit under measurement 100-1.
, And the other signal is input to a second circuit under test 100-2 having substantially the same characteristics as the circuit under test 100-1 and passed through the second circuit under test 100-2. The phase of the signal is shifted by 90 ° by the 90 ° phase shifter 3, and the signal whose phase is shifted by 90 ° is multiplied by the signal passed through the first circuit under measurement 100-1 by the phase detector 4, By supplying the multiplication result to the spectrum analyzer 6 via the low-pass filter 5, the circuit under measurement 100-1,
Determine the additional phase noise caused by 100-2. The measurement result at this time is hereinafter referred to as “measurement result A”. Measurement result A
Is represented by the above equation (11).

Subsequently, as shown in FIG. 1B, the signal from the signal source 1 is transmitted to the first circuit under test or the second circuit under test,
Further, the signal is passed through a third circuit to be measured (which is referred to as a circuit to be measured 100) having substantially the same characteristics as those described above, the passed signal is branched into two, and one of the signals is divided by 90 °.
After passing through the phase shifter 3, the other signal is multiplied by the phase detector 4, the phase noise of the measurement system is obtained based on the multiplication result, and the obtained result is referred to as “measurement result B”. Subtract from result A.

A circuit under test 1 is provided before the power splitter 2.
00 is connected, the output signal of the circuit under test 100 is expressed by equation (7), and the output of the
As, H (t) = Hsin ( 2ω't + 2φ 'REF, n (t) + φ DUT1, n (t) + φ 90, n (t)) + Hsin (φ 90, n (t)) ...... (12) Become. This is input to the spectrum analyzer 6 via the low-pass filter 5, and the power spectrum is observed. The measurement result B at this time is as follows: Sφ (f _m ) = [φ _{90, n} (f _m )] ² (13) Therefore, the exact noise per circuit to be measured can be obtained as [measurement result A−measurement result B] / 2.

FIG. 2 is a block diagram showing an embodiment of the measuring apparatus. Although the measurement shown in FIG. 1 can be performed by manually switching the circuit connection, the use of the apparatus shown in FIG. 2 facilitates the operation.

The apparatus comprises a signal source 1, a power splitter 3 for dividing the output of the signal source 1 into two signal paths,
A 90 ° phase shifter 3 disposed at one output of these two signal paths, a phase detector 4 for multiplying two signals passing through the two signal paths, and an output spectrum of the phase detector 4 It has a low-pass filter 5 and a spectrum analyzer 6 as observation means for observing.

Terminals 13 and 14 are provided on one of the two signal paths as connecting means for connecting a circuit to be measured (here, shown as circuits to be measured 100-1 and 100-2) to the two signal paths. Terminals 15 and 16
Are connected to connection terminals 13 ', 14', 15 ', 16' for connecting a circuit under test. That is, in one signal path, a signal is transmitted in the order of the terminal 13, the connection terminal 13 ', the circuit under test 100-1, the connection terminal 14', and the terminal 14, and in the other signal path, the terminal 1
5, the connection terminal 15 ', the circuit under test 100-2, the connection terminal 16', and the terminal 16 are transmitted in this order.

The feature of this embodiment is that the circuit to be measured is separated from the two signal paths, the portions thereof are short-circuited, and one of the circuits to be measured is connected between the signal source 1 and the power splitter 2. A switching circuit 7 between the terminals 13 to 16 and the connection terminals 13 'to 16' as a connection switching means for connecting to the terminal 11 connected to the switching circuit 7 between the signal source 1 and the power splitter 2. , 12 are provided.

The switching circuit 7 includes a plurality of interlocking switches. In the first state, the terminals 11 and 12, the terminal 13 and the connection terminal 13 ', the terminal 14 and the connection terminal 14', and the terminal 15
And the connection terminal 15 ', and the terminal 16 and the connection terminal 16'. In the second state, the terminal 11 and the connection terminal 1
3 ', terminal 12 and connection terminal 14', terminal 13 and terminal 1
4. Connect the terminal 15 and the terminal 16.

FIG. 3 is a block diagram showing a second embodiment of the additional phase noise measuring method.

In this embodiment, the circuits under test 100-1, 1
The measurement is shown in the case where the down-converters 8-1 and 8-2 are used for the respective outputs because the output frequency of 00-2 is high, and the amplifiers 9-1 and 9-2 are used in the subsequent stages.

In this case, first, as shown in FIG. 3A, one of the signals branched by the power splitter 2 is divided into a circuit under test 100-1, a down converter 8-1, and an amplifier 9.
-1 and the other signal to the circuit under measurement 100-2,
The signal passes through the down converter 8-2, the amplifier 9-2 and the 90 ° phase shifter 3, and the respective signals are input to the phase detection circuit 4. The output of the phase detection circuit 4 is observed by a spectrum analyzer 6 via a low-pass filter 5. Assuming that the measurement result at this time is A, the measurement result A is
The noise of the signal source 1 is canceled out, and the circuits under measurement 100-1, 1
00-2, down converters 8-1, 8-2, amplifier 9
-1, 9-2 and the sum of the noises added by the 90 ° phase shifter 3.

Next, as shown in FIG. 3B, the circuit under test 100-1 or 100-2 is disconnected, and one of them (hereinafter referred to as the circuit under test 100) is connected to the signal source 1 and the power splitter 2. And perform the same measurement. Assuming that the measurement result at this time is B, the measurement result B cancels the noises of the signal source 1 and the circuit under test 100, and downconverters 8-1, 8-2, amplifiers 9-1, 9-2, and 90 ° shows noise due to the phase shifter 3. Therefore, the accurate noise per circuit to be measured can be obtained as [measurement result A−measurement result B] / 2.

Further, as shown in FIG. 3 (c), the down converter 8-1 or 8-2 is cut off, and one of the down converters (hereinafter referred to as the down converter 8) is arranged in front of the power splitter 2, and Perform the measurement. Assuming that the measurement result at this time is C, this measurement result C is
1, 9-2 and the noise due to the 90 ° phase shifter 3 are shown. Therefore, the accurate noise per downconverter can be obtained as [measurement result B-measurement result C] / 2.

As described above, by sequentially providing the position where the power splitter is provided at the subsequent stage, it is possible to further separate the noise generated in the measurement system.

[0030]

As described above, the method and apparatus for measuring the additional phase noise of the present invention can separate the noise generated by the measuring system in the measurement of the additional phase noise, thereby enabling accurate measurement. effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an additional phase noise measuring method according to the present invention.

FIG. 2 is a block diagram showing an embodiment of an additional phase noise measuring apparatus according to the present invention.

FIG. 3 is a block diagram showing a second embodiment of the additional phase noise measuring method of the present invention.

FIG. 4 is a block diagram showing a conventional additional phase noise measuring method.

FIG. 5 is a block diagram showing a conventional additional phase noise measuring method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Signal source 2 Power splitter 3 90 degree phase shifter 4 Phase detector 5 Low pass filter 6 Spectrum analyzer 7 Switching circuit 8, 8-1, 8-2 Down converter 9, 9-1, 9-2 Amplifier 11- 16 terminals 13 'to 16' Connection terminals 100, 100-1, 100-2 Circuit under test

Claims (2)

(57) [Claims] 1. A signal for measurement is branched into two, one of the signals is input to a first circuit to be measured, and the other signal is input to a second circuit to be measured. The phase of the signal passing through the circuit under test is shifted by 90 ° by a 90 ° phase shifter, and the signal whose phase is shifted by 90 ° is multiplied by the signal passing through the first circuit under test. In an additional phase noise measuring method for obtaining additional phase noise generated by the first circuit under test and the second circuit under test using a result of the multiplication, the signal for the measurement is passed through a third circuit under test. The passed signal is branched into two, and one of the signals is passed through the 90 ° phase shifter and then multiplied by the other signal. The multiplication result is used to determine the phase noise of the measurement system. Phase noise is subtracted from the additional phase noise. Additional phase noise measurement method. 2. A signal source, a power splitter for distributing the output of the signal source into two signal paths, and 90 ° phase shifter disposed on one of the outputs of the two signal paths, the 90 ° shift The output signal of the phaser and the other of the two signal paths
Additional phase noise measurement, comprising: a phase detector that multiplies a signal passing through the phase detector; an observation unit that observes an output spectrum of the phase detector; and a connection unit that connects a circuit to be measured to each of the two signal paths. in the device, the connecting means, the connection switching for connecting one of both the circuit under test by shorting the part disconnect the two respective circuit to be measured from the signal path between the signal source and the power splitter An additional phase noise measuring device, characterized by including means.