For example, in a measurement system for data signal using a pulse pattern generator and an error detector, a phase controller apparatus which gives a desired delay to a clock signal is used.
As a delay device which gives a desired delay to a signal, there has been hitherto known a trombone-shaped delay device which varies the length of a signal line mechanically, for example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-163608.
The trombone-shaped delay device, however, has problems of upsizing and response speed.
When the frequency of a signal to be delayed varies in quite a wide range, for example, from 100 MHz to 10 GHz, the trombone-shaped delay device requires the movable range of wavelength for the minimum frequency and a desired resolution at the wavelength of the maximum frequency, hence to increase in size and need an extremely high mechanical accuracy.
On the other hand, as the delay device which gives a delay electronically, there is known a delay device using a quadrature modulator.
Generally, the quadrature modulator is used for a digital modulator which modulates a local signal of higher frequency with the two-phase of digital baseband signals I and Q.
The quadrature modulator may be used as the electronic delay device which gives direct current voltage instead of the baseband signals I and Q, thereby supplies and outputs the signal input as the local signal with the desired delay corresponding to the direct current voltage.
FIG. 11A is a block diagram showing the structure in a case that performing signal delaying by using the quadrature modulator as the phase controller apparatus according to the prior art.
As shown in FIG. 11A, in the quadrature modulator used as the electronic delay device, a first signal C as the local signal of frequency f is supplied to a 90-degree phase shifter 11.
The 90-degree phase shifter 11 divides the first signal C into two signals Ci and Cq which have a phase difference of 90 degrees from each other and outputs them.
The two signals Ci and Cq input from the 90-degree phase shifter 11 are output to each one end of a first mixer 12 and a second mixer 13.
Desired direct current voltages Vi and Vq satisfying the following relations are supplied to each another end of the first mixer 12 and the second mixer 13.Vi=cos θVq=sin θ
The respective outputs from the first mixer 12 and the second mixer 13 are combined with each other in an adder 14.
FIG. 11B is a vector diagram for use in describing an operation principle in a case that performing signal delaying by using the quadrature modulator as the phase controller apparatus according to the prior art.
As shown in FIG. 11B, by supplying the desired direct current voltages Vi and Vq satisfying the relation of Vi=cos θ and Vq=sin θ to the respective other ends of the first and second mixers 12 and 13 and combining them in the adder 14, a second signal C′ which is delayed only at a desired phase angle θ (unit is radian) against the first signal C can be obtained.
More specifically, when the two signals Ci and Cq having a phase difference of 90 degrees from each other are defined asCi=cos(2πft)=C Cq=sin(2πft),the second signal C′ output from the adder 14 becomes as follows.
                              C          ′                =                              Ci            ·            Vi                    +                      Cq            ·            Vq                                                  =                                                            cos                ⁡                                  (                                      2                    ⁢                                                                                  ⁢                    π                    ⁢                                                                                  ⁢                    ft                                    )                                            ·              cos                        ⁢                                                  ⁢            θ                    +                                                    sin                ⁡                                  (                                      2                    ⁢                                                                                  ⁢                    π                    ⁢                                                                                  ⁢                    ft                                    )                                            ·              sin                        ⁢                                                  ⁢            θ                                                  =                                            [                                                cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            +                      θ                                        )                                                  +                                  cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            -                      θ                                        )                                                              ]                        ⁢                          /                        ⁢            2                    -                                    [                                                cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            +                      θ                                        )                                                  -                                  cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            -                      θ                                        )                                                              ]                        ⁢                          /                        ⁢            2                                                  =                  cos          ⁡                      (                                          2                ⁢                                                                  ⁢                π                ⁢                                                                  ⁢                ft                            -              θ                        )                              
Therefore, the second signal C′ which is delayed at only the phase angle θ (the unit is radian) against the first signal C can be obtained.
By varying the direct current voltages Vi and Vq in the above-mentioned relation, the second signal C′ having a desired delay against the original first signal C can be obtained.
The phase angle θ is determined by a ratio of the direct current voltages Vi and Vq as below.θ=tan−1(Vq/Vi)
When the period of the first signal C is T,θ=2πτ/T is satisfied between the phase angle θ and the delay time τ.
Therefore, the second signal C′ may be expressed asC′=cos [(2π/T)(t−τ)].
Here, the (t−τ) defines the delay amount of the second signal C′ against the first signal C.
The quadrature modulator, however, has a quadrature error in the phase shifter 11, gain errors in the mixers 12 and 13, and an offset error independent of the direct current voltages Vi and Vq.
Therefore, it is necessary to compensate these errors in order to give the proper delay amount as (t−τ) to the second signal C′ obtained by the quadrature modulator.
For example, when there is a phase error φ in the phase shifter 11 on the side of the output signal Cq,Cq′=sin(2πft +φ)is satisfied and a second signal C″ at this time becomes as follows.
                              C          ″                =                                                            cos                ⁡                                  (                                      2                    ⁢                                                                                  ⁢                    π                    ⁢                                                                                  ⁢                    ft                                    )                                            ·              cos                        ⁢                                                  ⁢            θ                    +                                                    sin                ⁡                                  (                                                            2                      ⁢                                                                                          ⁢                      π                      ⁢                                                                                          ⁢                      ft                                        +                    ϕ                                    )                                            ·              sin                        ⁢                                                  ⁢            θ                                                  =                                            [                                                cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            +                      θ                                        )                                                  +                                  cos                  ⁡                                      (                                                                  2                        ⁢                                                                                                  ⁢                        π                        ⁢                                                                                                  ⁢                        ft                                            -                      θ                                        )                                                              ]                        ⁢                          /                        ⁢            2                    -                      [                                          cos                ⁡                                  (                                                            2                      ⁢                                                                                          ⁢                      π                      ⁢                                                                                          ⁢                      ft                                        +                    ϕ                    +                    θ                                    )                                            -                                                          ⁢                                                cos                  (                                                            2                      ⁢                                                                                          ⁢                      π                      ⁢                                                                                          ⁢                      ft                                        +                    ϕ                    -                    θ                                    ]                                ⁢                                  /                                ⁢                2                                                                                      =                                    A              ·                              cos                ⁡                                  (                                                            2                      ⁢                                                                                          ⁢                      π                      ⁢                                                                                          ⁢                      ft                                        -                    θ                    +                                          ϕ                      ⁢                                              /                                            ⁢                      2                                                        )                                                      +                          B              ·                              sin                ⁡                                  (                                                            2                      ⁢                                                                                          ⁢                      π                      ⁢                                                                                          ⁢                      ft                                        ⁢                                                                                  +                    θ                    +                                          ϕ                      ⁢                                              /                                            ⁢                      2                                                        )                                                                    ⁢                                  ⁢                  where          ,                      A            =                          cos              ⁡                              (                                  ϕ                  ⁢                                      /                                    ⁢                  2                                )                                              ,                      B            =                          sin              ⁡                              (                                  ϕ                  ⁢                                      /                                    ⁢                  2                                )                                                        
As a result, in the second signal C″ obtained by the above formula decreases in amplitude by the phase error φ compared with the ideal second signal C′ as described above, and it becomes such a configuration that the signal in the first term with the phase advanced by φ/2 overlaps with the signal in the second term of the phase totally different from that of the first term.
Further, since the frequency of the first term is equal to the frequency of the second term in the above formula, the first term and the second term cannot be separated even when it passes through a filter.
When there is an offset error independent of the direct current voltages Vi and Vq in the quadrature modulator, an error occurs in the phase delay of the signal obtained by applying the direct current voltages Vi and Vq.
In order to compensate these errors in the quadrature modulator, for example, a technique about a carrier quadrature error detection method of the quadrature modulator and a quadrature modulating device disclosed in US2004/0250192A1 may be adopted.
In the carrier quadrature error detection method of the quadrature modulator according to the US2004/0250192A1, in a state that the signal levels of the I and Q signals are each made to be zero, a pair of direct current voltages for causing the modulating signal output from the quadrature modulator to be a predetermined reference level, are each added to the I and Q signals. In a state that pairs of direct current voltages are each changed and sequentially added to the I and Q signals, plural combinations of pairs of direct current voltages for making a signal level of the modulating signal output from the quadrature modulator at the predetermined reference level, are retrieved. Then, the quadrature error is calculated from simultaneous equations in which respective values of the retrieved plural combinations of pairs of direct current voltages, the signal level of the modulating signal output from the quadrature modulator, and a quadrature error of the carrier signals are defined as variables.
Since each error of the quadrature modulator shows frequency dependence, it is very difficult to cope with the error according to the technique disclosed in the US2004/0250192A1 when the frequency of the signal to be controlled varies in a wide range as described above.
Therefore, when realizing the pulse pattern generator and the error detector using the quadrature modulator as the phase controller apparatus, it is very difficult to realize them with a high accuracy, respectively.