Abstract:
Provided are an integrated dielectric resonator filter and a clock extraction device using the integrated dielectric resonator filter. The integrated dielectric resonator filter includes: a microwave substrate; a disc type dielectric resonator installed on the microwave substrate and having predetermined diameter and height; an input and output transmission line installed on both sides of the disc type dielectric resonator to transmit input and output signals; and a metal cover enclosing the disc type dielectric resonator to form a predetermined volume, opened toward the input and output transmission line, and closed in an orthogonal direction to the input and output transmission line.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the benefit of Korean Patent Application No. 10-2005-0110182, filed on Nov. 17, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a dielectric resonator filter adopted in an receiver for the ultrahigh optical transmission system and a clock extraction device using the same, and more particularly, to an electric filter extracting a clock signal from the received data to reproduce a clock signal in an optical receiver and an open-loop type clock extraction device using the same. 
   2. Description of the Related Art 
   Clock extraction devices are slightly differently constituted according to types of used transmission signals. In a case where NRZ signals are used, signals corresponding to clock frequencies do not exist. Thus, the clock extraction devices additionally include nonlinear circuit blocks to generate clock signal components. In a case where RZ signals including components of clock signals are used, the clock extraction devices don&#39;t need nonlinear circuit blocks. 
   Clock extraction devices for optical communication systems require electric filter blocks to extract high-quality clock signals and can be classified into closed-loop structure using phase-locked loops (PLLs) and open-loop structure using passive bandpass filters (BPFs). 
   The open-loop devices include simpler circuit structures and can be implemented more easily at a transmission speed of Gb/s or more as compared to the closed-loop devices. Also, in the open-loop devices, some different techniques have been adopted for the passive BPFs depending on transmission speeds of systems. SAW filter or tank circuit using lumped R, L, and C has been used at a transmission of Gb/s or less. Disc type dielectric resonator filter, which has high-Q value in microwave frequencies, has been used at a transmission of several Gb/s or more. 
   However, the disc type dielectric resonator filter has been manufactured in the form of independent module with the input and output coaxial connectors. Thus, the conventional disc type dielectric resonator filter is difficult to integrate with other electrical circuits, such as nonlinear circuits and clock amplifiers, in a clock extraction device. Nonlinear circuit blocks and clock amplifier blocks realized on a microwave substrate have been separately manufactured in the form of individual modules in which the input and output connectors are installed, too. 
   Accordingly, conventional dielectric resonator filters hinder open-loop clock extraction devices using dielectric resonator filters from being compact. Thus, these configurations using the individual modules increase total connection paths in the open-loop clock extraction devices. As a result, the signal loss increases. 
   Also, in a case of several Gb/s clock extraction devices using the conventional dielectric resonator filters, a plurality of undesired spurious pass bands exist in the vicinity of central frequencies of the conventional dielectric resonator filters that mean clock frequencies. Thus, additional BPFs are required to remove the undesired spurious pass bands. 
   SUMMARY OF THE INVENTION 
   The present invention provides a dielectric resonator filter, in which the input and output ports are realized by micro-strip transmission lines, and an open-loop type clock extraction device using the dielectric resonator filter. 
   According to an aspect of the present invention, there is provided a dielectric resonator filter including: a microwave substrate; a disc type dielectric resonator installed on the microwave substrate and having predetermined diameter and height; an input and output transmission line installed on both sides of the disc type dielectric resonator to transmit input and output signals; and a metal cover enclosing the disc type dielectric resonator to form a predetermined volume, opened toward the input and output transmission line, and closed in an orthogonal direction to the input and output transmission line. 
   According to another aspect of the present invention, there is provided a clock extraction device of a receiver including: a dielectric resonator filter extracting a clock signal from the input signal transmitted to a disc type dielectric resonator through an input transmission line on a substrate and comprising a metal cover enclosing the disc type dielectric resonator to form a predetermined volume so as to set a resonator frequency, which is equal to the clock frequency; and a monolithic microwave integrated circuit amplifier directly connected to an output transmission line of the dielectric resonator filter through bonding and amplifying the clock signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a block diagram of a general open-loop type clock extraction device for extracting a clock signal from an NRZ signal; 
       FIG. 2  is a block diagram of a general open-loop type clock extraction device for extracting a clock signal from an RZ signal; 
       FIG. 3  is a circuit diagram of a nonlinear circuit unit using a pair of diodes and a power combiner having a phase difference of 90°; 
       FIG. 4  is a view illustrating a nonlinear circuit unit using an EX-OR and a pair of delay lines having a time difference of T/2; 
       FIG. 5  is a view illustrating a conventional dielectric resonator filter used in an open-loop type clock extraction device; 
       FIG. 6  is a view illustrating an integrated dielectric resonator filter according to an embodiment of the present invention; 
       FIG. 7  is a view illustrating a clock extraction device using an integrated dielectric resonator filter according to an embodiment of the present invention; 
       FIGS. 8A through 8F  are graphs illustrating a process of extracting a 40 GHz clock signal using a 40 Gb/s clock extraction device shown in  FIG. 7 ; 
       FIG. 9  is a graph illustrating a wide band frequency response characteristic of an integrated dielectric resonator filter adopted in a clock extraction device for the transmission speed of 40 Gb/s according to an embodiment of the present invention; 
       FIG. 10  is a graph illustrating a wide band frequency response characteristic of the conventional dielectric resonator filter of  FIG. 5  used in a clock extraction device for the transmission speed of 20 Gb/s; and 
       FIG. 11  is a flowchart of an operation of a clock extraction device using an integrated dielectric resonator filter according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, the present invention will be described in detail with reference to the attached drawings. 
     FIG. 1  is a block diagram of a general open-loop type clock extraction device for extracting a clock signal from an NRZ signal. Referring to  FIG. 1 , the general open-loop type clock extraction device includes a nonlinear circuit block  100  converting a received NRZ signal into a PRZ signal from which clock information is generated, an electric filter block  110  extracting a clock signal component from the PRZ signal, and a clock amplifier block  120  amplifying the clock signal. 
     FIG. 2  is a block diagram of a general open-loop type clock extraction device for extracting a clock signal from an RZ signal. Referring to  FIG. 2 , the general open-loop type clock extraction device includes an electric filter block  200  and a clock amplifier block  210 . 
     FIG. 3  is a circuit diagram of a nonlinear circuit unit using a pair of diodes and a power combiner having a phase difference of 90°. Referring to  FIG. 3 , the nonlinear circuit unit includes a wide band amplifier  300 , a low pass filter (LPF)  310 , a pair of diodes  320  and  330 , and a power combiner  340  and  350  having a input phase difference of 90°. 
     FIG. 4  is a view illustrating a nonlinear circuit unit using an EX-OR and a pair of delay lines having a time difference of T/2. Referring to  FIG. 4 , the nonlinear circuit unit includes an input transmission line  410 , an output transmission line  460 , a power divider using three resistors  420 , two transmission lines  430  and  440  having different lengths to make T/2 time difference, and an EX-OR logic device  450 . 
     FIG. 5  is a view illustrating a conventional dielectric resonator filter used in an open-loop type clock extraction device. Referring to  FIG. 5 , the conventional dielectric resonator filter includes a microwave substrate  530 , an input connector  500 , an output connector  540 , an input transmission line  510 , an output transmission line  515 , a dielectric resonator  520 , a cylindrical metallic module case  550 , and a metallic screw  560  for adjusting a resonant frequency. The metallic screw  560  is inserted to easily adjust a resonant frequency of a BPF. 
   However, in the conventional dielectric resonator filter shown in  FIG. 5 , undesired spurious pass bands (17.8 GHz, 22.8 GHz, and 24.7 GHz) exist in the vicinity of a clock frequency of 19.906 GHz of a 20 Gb/s transmission signal as shown with a frequency response characteristic of a 20 GHz band dielectric resonator filter shown in  FIG. 10 . Thus, in a case where such a conventional dielectric resonator filter is adopted in a clock extraction device, an additional device such as a BPF is required to remove the undesired spurious pass bands. 
     FIG. 6  is a view illustrating an integrated dielectric resonator filter according to an embodiment of the present invention. 
   Referring to  FIGS. 6A through 6C , the integrated dielectric resonator filter includes a metal plate  620  fixing a metallic cover  650  and a microwave substrate  630 , a microwave substrate  630 , an input transmission line  640 , an output transmission line  645 , a disc type dielectric resonator  600 , a metallic cover  650 , and metallic screws  610  coupling a metallic cover  650  to a plate  620 . Physical sizes of a dielectric resonator, a metallic cover, and input and output excitation transmission lines vary with a desired resonant frequency of the bandpass filter. The design values in 40 GHz band will be taken as an example. 
   The microwave substrate  630  has a dielectric constant of 2.33, a thickness of 0.254 mm, and a width (W) of 2.4 mm as shown in  FIG. 6C . The input and output transmission lines  640  and  645  on the microwave substrate  630  are micro-strip transmission lines having a width of 0.37 mm, and a length L ( FIG. 6B ) of the microwave substrate  630  in a transmission line length direction is 14 mm. The disc type dielectric resonator  600  has a dielectric constant of 30.7, a diameter of 1.6 mm, and a height of 0.64 mm. The metallic cover  650  has an internal height H ( FIG. 6C ) of 1.65 mm from an upper surface of the microwave substrate  630  and a length l ( FIG. 6B ) of 8 mm. 
   A dielectric resonator filter according to the present invention does not include a metallic screw for adjusting the resonant frequency as shown in  FIG. 5  because an insertion of the metallic screw deteriorates spurious characteristics. In this integrated dielectric resonator filter, the resonant frequency can be adjusted by adjusting a height of a dielectric resonator or the internal height H of the metal cover  650  from the microwave substrate  630  as shown in  FIG. 6C . 
   Also, a metallic cover according to the present invention has a C-shaped simple structure and thus can be easily fabricated and simply attached and/or detached through coupling screws. 
   In the present invention, the precise adjustment of a resonant frequency is achieved by reducing a height of a dielectric resonator. The measurement of the resonant frequency of the filter is achieved under condition of installing a metallic cover so as to form the predetermined cavity enclosing the dielectric resonator. 
   In an integrated dielectric resonator filter according to the present invention, after the input and output transmission lines of this filter is connected to the input and output transmission lines of the other electrical circuit through bonding without a coaxial input and output connector, the resonant frequency of this filter does not vary. Thus, the integrated dielectric resonator filter can be inserted among the other circuit blocks. 
     FIG. 7  is a view illustrating a structure of a clock extraction device using an integrated dielectric resonator filter according to an embodiment of the present invention. 
   The clock extraction device includes three substrate blocks that are a nonlinear circuit block  710 , an electric filter block  720 , and a clock amplifier block  730 , as shown in  FIG. 7 . The nonlinear circuit block  710  and the clock amplifier block  730  except the electric filter block  720  may be manufactured using general methods. However, a clock extraction device according to the present invention may include an electric filter block as an integrated dielectric resonator filter. Thus, according to a constituting and manufacturing methods according to the present invention, the total blocks of an open-loop type clock extraction device using a dielectric resonator filter can be integrated into a module package. Finally, the clock extraction device can be manufactured as a compact single module. 
     FIGS. 8A through 8F  are graphs illustrating a process of extracting a 40 GHz clock signal from a 40 Gb/s NRZ signal using the clock extraction device shown in  FIG. 7 . 
     FIG. 8A  is a graph illustrating the waveform of an input NRZ electric signal into a 40 Gb/s clock extraction device. A transmission speed of an input signal is accurately 39.81312 Gb/s according to STM-256 standards.  FIG. 8B  is a graph illustrating the output waveform in the nonlinear circuit block in the 40 Gb/s clock extraction device. As shown in  FIG. 8B , the input NRZ signal shown in  FIG. 8A  is converted into the PRZ signal including the clock signal component. 
     FIG. 8C  is a graph illustrating the output waveform of the integrated dielectric resonator filter, i.e., the waveform of a 39.81312 GHz clock signal.  FIG. 8D  is a graph illustrating the final waveform of the clock signal that is amplified by the MMIC amplifier block, which is followed by the integrated dielectric resonator filter, as shown in  FIG. 7 . The amplitude of the clock signal is increased from 372 mVpp to 2.5 Vpp through the MMIC amplifier block as compared to the signal of  FIG. 8C . The RMS jitter value is decreased from 386 fs(RMS) to 278 fs(RMS). 
     FIGS. 8E and 8F  are graphs illustrating the spectrum of the clock signal shown in  FIG. 8D . As shown in  FIG. 8E , other frequency components except a clock frequency signal do not exist in a wide band.  FIG. 8F  represents the narrow band spectrum characteristic and means the noise characteristic of the extracted clock signal. The differences between the noise level and the clock component are 70.5 dB and 98.54 dB at a distance of 10 kHz and 100 kHz from the frequency of the clock signal, respectively. 
     FIG. 9  is a graph illustrating the wide band frequency response of the integrated dielectric resonator filter used in the 40 Gb/s clock extraction device shown in  FIG. 7 . 
   The dielectric resonator filter extracts a clock signal of 39.81312 GHz from a 39.81312 Gb/s transmission signal that is an STM-256 signal. As shown in  FIG. 9 , any spurious pass band except the clock frequency of 39.81312 GHz does not exist in the vicinity of the center frequency of 39.81312 GHz and in a full wide band of 45 GHz as compared to a graph of  FIG. 10 . 
     FIG. 10  is a graph illustrating the wide-band frequency response of the conventional dielectric resonator filter of  FIG. 5  used for a 20 Gb/s clock extraction device. 
   Undesired spurious pass bands of 17.8 GHz, 22.8 GHz, and 24.7 GHz exist in the vicinity of a clock frequency of 19.90656 GHz. 
   Such spurious pass bands deteriorate the quality of an extracted clock signal. Thus, the clock extraction device requires another filter block removing the spurious pass bands after a dielectric resonator filter. As a result, an open-loop type clock extraction circuit cannot be compact. 
     FIG. 11  is a flowchart of an operation principle of a clock extraction device using a dielectric resonator filter according to an embodiment of the present invention. 
   In operation S 1100 , a nonlinear circuit block receives NRZ data and converts the NRZ data into a PRZ signal from which clock information has been generated. In operation S 1110 , an integrated dielectric resonator filter extracts a clock signal from the PRZ signal. In operation S 1120 , an MMIC amplifier amplifies the clock signal extracted from an integrated dielectric resonator filter. 
   As described above, the open-loop type clock extraction device including a dielectric resonator filter can be integrated into a compact module by applying the integrated dielectric resonator filter with the input and output ports realized by micro-strip transmission lines according to the present invention. Also, the compact clock extraction device is advantageous to a receiver of an ultrahigh optical transmission system. In addition, the signal loss can be minimized due to the decrease of the total signal path in the clock extraction device. Moreover, an additional BPF to remove the spurious pass bands is not required in the present invention. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.