Patent Publication Number: US-2023142553-A1

Title: Frequency mixer including non-linear circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2021-0152302 filed on Nov. 8, 2021, and 10-2022-0023220 filed on Feb. 22, 2022, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     BACKGROUND 
     Embodiments of the present disclosure described herein relate to a frequency mixer, and more particularly, relate to a frequency mixer including a non-linear circuit. 
     A frequency mixer is a device for mixing different frequency signals. For example, the frequency mixer may generate a frequency output signal corresponding to the sum or difference of different frequency input signals by using the non-linear characteristic. A frequency mixer that generates a frequency output signal corresponding to the sum of different frequency input signals may be referred to as an up-conversion frequency mixer. A frequency mixer that generates a frequency output signal corresponding to a difference between different frequency input signals may be referred to as a down-conversion frequency mixer. 
     The frequency mixer may be used in various electronic systems based on wireless communication. The degradation of the frequency mixer may cause a decrease in signal sensitivity, data loss, an increase in the error rate, and the like in electronic systems. Examples of quality factors of a frequency mixer include insertion loss, linearity, port-to-port isolation, and the like. In an electronic system including a frequency mixer, a frequency mixer with improved quality factors such as insertion loss, linearity, and port-to-port isolation may be required to ensure signal sensitivity improvement, reliability improvement, and the like. 
     SUMMARY 
     Embodiments of the present disclosure provide a frequency mixer including a non-linear circuit. 
     According to an embodiment, a frequency mixer includes a first matching circuit that generates a matched local oscillator (LO) signal based on an LO signal, a non-linear circuit that generates a non-linear LO signal based on the matched LO signal, a second matching circuit that generates a matched radio frequency (RF) signal based on an RF signal, a mixing circuit that generates a mixed signal based on a mixing of the non-linear LO signal and the matched RF signal, a third matching circuit that generates an intermediate frequency (IF) signal based on the mixed signal, wherein the non-linear circuit includes a non-linear transistor, a bias transistor, and an internal matching circuit connected in series. 
     In an embodiment, the internal matching circuit may include a resistor, an inductor and a capacitor which are connected in parallel. 
     In an embodiment, a resistance of the resistor, an inductance of the inductor, and a capacitance of the capacitor may be optimized to enhance at least one of an LO-to-RF isolation, an RF-to-LO isolation and an LO-to-IF isolation of the frequency mixer. 
     In an embodiment, the bias transistor may operate in response to a bias voltage, and a level of the bias voltage may be optimized to enhance at least one of an LO-to-RF isolation, an RF-to-LO isolation and an LO-to-IF isolation of the frequency mixer. 
     In an embodiment, the bias transistor may operate in response to a bias voltage, and a level of the bias voltage may be optimized to enhance at least one of an LO-to-RF isolation, an RF-to-LO isolation and an LO-to-IF isolation of the frequency mixer for a process change of an active element and a process change of a passive element occurring in a process of manufacturing the frequency mixer. 
     In an embodiment, the non-linear circuit may be connected between a terminal through which the non-linear LO signal is generated and a first node to operate in response to the matched LO signal, wherein the bias transistor may be connected between the first node and a second node to operate in response to a bias voltage, and the internal matching circuit may be connected between the second node and a ground node. 
     In an embodiment, the non-linear circuit may further include a bias voltage source configured to provide the bias voltage to a gate terminal of the bias transistor. 
     In an embodiment, the internal matching circuit may include a resistor connected between the second node and the ground node, an inductor connected between the second node and the ground node, and a capacitor connected between the second node and the ground node. 
     In an embodiment, a drain terminal of the non-linear transistor may be connected to the terminal through which the non-linear LO signal is generated, and a source terminal of the non-linear transistor may be connected to the first node, wherein a drain terminal of the bias transistor may be connected to the first node and a source terminal of the bias transistor may be connected to the second node. 
     In an embodiment, each of the non-linear transistor and the bias transistor may be implemented with at least one of an N-channel metal oxide semiconductor (NMOS) transistor, a GaAs pseudomorphic high electron mobility transistor (PHEMT), a GaAs metamorphic high electron mobility transistor (MHEMT), an InP high electron mobility transistor (HEMT), and a GaN field effect transistor (FET). 
     In an embodiment, the frequency mixer may include a down-conversion frequency mixer that generates the IF signal having a third frequency obtained by subtracting a second frequency of the LO signal from a first frequency of the RF signal. 
     According to another embodiment, a frequency mixer matches a local oscillator (LO) signal, generates a non-linear LO signal based on a matched LO signal, and generates an intermediate frequency (IF) signal based on the non-linear LO signal and a radio frequency (RF) signal. The frequency mixer includes a first transistor connected between a terminal through which the non-linear LO signal is generated and a first node to operate in response to the matched LO signal, a second transistor connected between the first node and a second node to operate in response to a bias voltage, and an internal matching circuit connected between the second node and a ground node. 
     In an embodiment, the internal matching circuit may include a resistor connected between the second node and the ground node, an inductor connected between the second node and the ground node, and a capacitor connected between the second node and the ground node. 
     In an embodiment, a resistance of the resistor, an inductance of the inductor, and a capacitance of the capacitor may be optimized to enhance at least one of an LO-to-RF isolation, an RF-to-LO isolation and an LO-to-IF isolation of the frequency mixer. 
     In an embodiment, the frequency mixer may further include a bias voltage source that provides the bias voltage to a gate terminal of the second transistor. 
     In an embodiment, a level of the bias voltage may be optimized to enhance at least one of an LO-to-RF isolation, an RF-to-LO isolation and an LO-to-IF isolation of the frequency mixer for a process change of an active element and a process change of a passive element occurring in a process of manufacturing the frequency mixer. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The above and other objects and features of the present disclosure will become apparent by describing in detail embodiments thereof with reference to the accompanying drawings. 
         FIG.  1    is a block diagram illustrating a frequency mixer according to an embodiment of the present disclosure; 
         FIG.  2    is a circuit diagram illustrating a general non-linear circuit; 
         FIG.  3    is a circuit diagram illustrating the non-linear circuit of  FIG.  1    according to some embodiments of the present disclosure; 
         FIG.  4    is a diagram illustrating frequency signals of the non-linear circuit of  FIG.  2   ; 
         FIG.  5    is a diagram illustrating frequency signals of the non-linear circuit of  FIG.  3   ; 
         FIG.  6    is a graph illustrating insertion loss characteristics according to some embodiments of the present disclosure; 
         FIG.  7    is a graph illustrating LO-to-RF isolation according to some embodiments of the present disclosure; 
         FIG.  8    is a graph illustrating RF-to-LO isolation according to some embodiments of the present disclosure; and 
         FIG.  9    is a graph illustrating LO-to-IF isolation according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various embodiments of the present disclosure will be described clearly and in detail, so that those skilled in the art can easily carry out the present disclosure. 
     Terms such as “unit” and “module” used below or functional blocks shown in the drawings may be implemented in the form of software, hardware or a combination thereof. Hereinafter, in order to clearly explain the technical spirit of the present disclosure, duplicate descriptions of the same components may be omitted. 
       FIG.  1    is a block diagram illustrating a frequency mixer according to an embodiment of the present disclosure. Referring to  FIG.  1   , a frequency mixer  100  may generate an intermediate frequency (IF) signal based on a radio frequency (RF) signal and a local oscillator (LO) signal. 
     The frequency mixer  100  may be a device for mixing different frequency signals. For example, the frequency mixer  100  may be implemented as an up-conversion frequency mixer that generates a frequency output signal corresponding to the sum of different frequency input signals by using non-linearity. Alternatively, the frequency mixer  100  may be implemented as a down-conversion frequency mixer that generates a frequency output signal corresponding to a difference between different frequency input signals using non-linearity. 
     When the frequency mixer  100  is implemented as an up-conversion frequency mixer, the frequency mixer  100  may generate an IF signal having a frequency obtained by adding the frequency of the LO signal to the frequency of the RF signal. 
     When the frequency mixer  100  is implemented as a down-conversion frequency mixer, the frequency mixer  100  may generate an IF signal having a frequency obtained by subtracting the frequency of the LO signal from the frequency of the RF signal. 
     The frequency mixer  100  may include an LO matching circuit  110 , a non-linear circuit  120 , an RF matching circuit  130 , a mixing circuit  140 , and an IF matching circuit  150 . 
     The LO matching circuit  110  may receive the LO signal through an LO port. The LO matching circuit  110  may generate a matched LO (MLO) signal based on the LO signal. The LO matching circuit  110  may provide the MLO signal to the non-linear circuit  120 . 
     The non-linear circuit  120  may receive the MLO signal from the LO matching circuit  110 . The non-linear circuit  120  may generate a non-linear LO (NLO) signal based on the MLO signal. The NLO signal may be a signal that is obtained by modulating the MLO signal based on non-linearity. The non-linear circuit  120  may provide an NLO signal to the mixing circuit  140 . 
     In some embodiments, the non-linear circuit  120  may include a first transistor, a second transistor, and an internal matching circuit connected in series. Based on the circuit structure of the non-linear circuit  120 , quality factors such as insertion loss, isolation between ports, and the like may be improved. 
     For example, the frequency mixer  100  may be used in various wireless communication-based electronic systems. The frequency mixed by the frequency mixer  100  may be used for wireless communication. Degradation of frequency mixers may lead to reduced signal sensitivity, data loss, and increased error rates in electronic systems. As examples of quality factors of a frequency mixer, there are insertion loss, linearity, port-to-port isolation, and the like. By improving the quality factors based on the circuit structure of the non-linear circuit  120 , it is possible to improve the communication performance of the electronic system including the frequency mixer. The details of the non-linear circuit  120  will be described below with reference to  FIG.  3   . 
     The RF matching circuit  130  may receive an RF signal through an RF port. The RF matching circuit  130  may generate a matched RF (MRF) signal based on the RF signal. The RF matching circuit  130  may provide the MRF signal to the mixing circuit  140 . 
     The mixing circuit  140  may receive the NLO signal from the non-linear circuit  120 . The mixing circuit  140  may receive the MRF signal from the RF matching circuit  130 . The mixing circuit  140  may generate a mixed (MX) signal based on the mixing of the NLO signal and the MRF signal. The mixing circuit  140  may provide the MX signal to the IF matching circuit  150 . 
     The IF matching circuit  150  may generate an IF signal based on the MX signal. The IF matching circuit  150  may provide the IF signal to an IF port. 
       FIG.  2    is a circuit diagram illustrating a general non-linear circuit. Referring to  FIG.  2   , a circuit diagram of a general non-linear circuit (NLC) is illustrated. The general non-linear circuit NLC may correspond to the non-linear circuit  120  of  FIG.  1    according to an embodiment of the present disclosure. The general non-linear circuit NLC is only described to help the understanding of the non-linear circuit  120  of the present disclosure, and the general non-linear circuit NLC may include other components that do not constitute the related literature. 
     The general non-linear circuit NLC may generate an NLO signal based on the MLO signal. For example, the general non-linear circuit NLC may receive an MLO signal from the LO matching circuit  110  of  FIG.  1   , generate the NLO signal based on the MLO signal, and provide the NLO signal to the mixing circuit  140  of  FIG.  1   . 
     The general non-linear circuit NLC may include a non-linear transistor AM. The non-linear transistor AM may be connected between the terminal through which the NLO signal is generated and a ground node GND. The non-linear transistor AM may operate in response to the MLO signal. That is, the non-linear transistor AM may non-linearly modulate the MLO signal to generate the NLO signal. 
       FIG.  3    is a circuit diagram illustrating the non-linear circuit of  FIG.  1    according to some embodiments of the present disclosure. Referring to  FIGS.  1  and  3   , a circuit diagram of the non-linear circuit  120  according to some embodiments of the present disclosure is shown. The non-linear circuit  120  may correspond to the non-linear circuit  120  of  FIG.  1   . 
     The non-linear circuit  120  may generate the NLO signal based on the MLO signal. For example, the non-linear circuit  120  may receive the MLO signal from the LO matching circuit  110 , generate the NLO signal based on the MLO signal, and provide the NLO signal to the mixing circuit  140 . 
     The non-linear circuit  120  may include the non-linear transistor AM, a bias transistor BM, an internal matching circuit IMC, and a bias voltage source Vb. The non-linear transistor AM, the bias transistor BM and the internal matching circuit IMC may be connected in series. The non-linear transistor AM and the bias transistor BM may also be referred to as a first transistor and a second transistor, respectively. 
     The non-linear transistor AM may be connected between a terminal through which the NLO signal is generated and a first node N 1 . The non-linear transistor AM may operate in response to the MLO signal. That is, the non-linear transistor AM may non-linearly modulate the MLO signal to generate the NLO signal. 
     In some embodiments, the non-linear transistor AM may be implemented as an N-channel metal oxide semiconductor (NMOS) transistor. For example, a source node, a gate node, and a drain node of the non-linear transistor AM may be connected to the first node N 1 , a terminal for receiving an MLO signal, and a terminal for generating an NLO signal, respectively. 
     The bias transistor BM may be connected between the first node N 1  and a second node N 2 . The bias transistor BM may operate in response to a bias voltage. For example, the bias transistor BM may receive the bias voltage from the bias voltage source Vb. The bias voltage may be a gate bias capable of turning on or off the bias transistor BM. As the bias transistor BM is turned on or off according to the bias voltage, parasitic component values of the bias transistor BM may vary. 
     In addition, the bias voltage may be determined as one of several voltage values greater than or equal to a threshold voltage of the bias transistor BM. The bias voltage may be adjusted to improve the isolation of the frequency mixer  100  in consideration of the parasitic component values of the bias transistor BM and the combined impedance value of the internal matching circuit IMC connected to the bias transistor BM. 
     For example, the bias transistor BM may be adjusted to allow a specific frequency component of the electrical signal output from the non-linear transistor AM to escape through the internal matching circuit IMC according to the bias voltage, so that it is possible to attenuate a frequency component transmitted between different ports (e.g., LO, RF and IF ports) of the frequency mixer  100 . That is, the bias transistor BM may enable matching between different frequency signals (RF signal, LO signal, and IF signal). 
     The bias voltage source Vb may be connected to the bias transistor BM and the ground node GND. The bias voltage source Vb may provide a bias voltage to the bias transistor BM. 
     In some embodiments, the bias transistor BM may be implemented as an NMOS transistor. For example, a source node, a gate node, and a drain node of the bias transistor BM may be connected to the second node N 2 , the bias voltage source Vb and the first node N 1 , respectively. 
     In some embodiments, the bias transistor BM may improve the isolation of the frequency mixer  100 . For example, the level of the bias voltage provided to the gate terminal of the bias transistor BM may be optimized to improve at least one of the LO-to-RF isolation, the RF-to-LO isolation and the LO-to-IF isolation of the frequency mixer  100 . 
     In some embodiments, each of the non-linear transistor AM and the bias transistor BM may be implemented with at least one of an N-channel metal oxide semiconductor (NMOS) transistor, a GaAs pseudomorphic high electron mobility transistor (PHEMT), a GaAs metamorphic high electron mobility transistor (MHEMT), an InP high electron mobility transistor (HEMT), and a GaN field effect transistor (FET). 
     The LO-to-RF isolation may refer to the degree at which the propagation of frequency components is blocked between the LO port and the RF port. The RF-to-LO isolation may refer to the degree at which propagation of frequency components is blocked between the RF port and the LO port. The LO-to-IF isolation may refer to a degree at which propagation of frequency components is blocked between the LO port and the IF port. 
     In some embodiments, the bias transistor BM may improve the isolation of the frequency mixer  100  in consideration of a process change according to a manufacturing process. For example, the level of the bias voltage provided to the gate terminal of the bias transistor BM may be optimized to improve at least one of the LO-to-RF isolation, the RF-to-LO isolation and the LO-to-IF isolation of the frequency mixer  100  with respect to the process change of the active element and the process change of the passive element occurring in the manufacturing process of the frequency mixer  100 . 
     The internal matching circuit IMC may be connected between the second node N 2  and the ground node GND. The internal matching circuit IMC may improve the isolation of the frequency mixer  100  by outputting a specific frequency component of the electrical signal transmitted from the non-linear transistor AM through the bias transistor BM to the ground node GND. 
     In some embodiments, the internal matching circuit IMC may be implemented as an RLC parallel circuit. For example, the internal matching circuit IMC may include a resistor R, an inductor L and a capacitor C connected in parallel between the second node N 2  and the ground node GND. 
     In some embodiments, the magnitude of the combined impedance of the internal matching circuit IMC may be optimized to improve the isolation of the frequency mixer  100 . For example, the internal matching circuit IMC may include the resistor R, the inductor L and the capacitor C connected in parallel. The resistance of the resistor R, the inductance of the inductor L and the capacitance of the capacitor C may be optimized to improve at least one of the LO-to-RF isolation, RF-to-LO isolation and LO-to-IF isolation of the frequency mixer  100 . 
       FIG.  4    is a diagram illustrating frequency signals of the non-linear circuit of  FIG.  2   . Referring to  FIGS.  2  and  4   , spectral characteristics according to frequencies of an IF signal, an RF signal and an LO signal of a frequency mixer including a general non-linear circuit NLC will be described with reference to graphs. In the graphs, the horizontal axis represents the frequency, and the vertical axis represents the power level. 
     According to the simulation conditions, the frequency of the RF signal is 140 GHz, the frequency of the LO signal is 139 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     With reference to the graph of the IF signal, the LO-to-IF isolation will be described. When the frequency of the LO signal is 139 GHz and the magnitude of the LO signal is −10 dBm, a measurement point MPa 1  represents −25.629 dBm as a spectral value of the IF signal. Therefore, the LO-to-IF isolation may be calculated as ‘−10-(−25.629) dBm’. That is, the LO-to-IF isolation is 15.629 dBm. 
     With reference to the graph of an RF signal, the LO-to-RF isolation will be described. When the frequency of the LO signal is 139 GHz and the magnitude of the LO signal is −10 dBm, a measurement point MPa 2  represents −27.687 dBm as a spectrum value of the RF signal. Therefore, the LO-to-RF isolation may be calculated as ‘−10-(−27.689) dBm’. That is, the LO-to-RF isolation is 17.689 dBm. 
     With reference to the graph of the LO signal, the RF-to-LO isolation will be described. When the frequency of the RF signal is 140 GHz and the magnitude of the RF signal is −30 dBm, a measurement point MPa 3  represents −48.521 dBm as a spectral value of the LO signal. Therefore, the RF-to-LO isolation may be calculated as ‘−30-(−48.521) dBm’. That is, the RF-to-LO isolation is 18.521 dBm. 
       FIG.  5    is a diagram illustrating frequency signals of the non-linear circuit of  FIG.  3   . Referring to  FIGS.  3  and  5   , according to embodiments of the present disclosure, spectral characteristics according to frequencies of an IF signal, an RF signal and an LO signal of the frequency mixer  100  including the non-linear circuit  120  will be described with reference to graphs. In the graphs, the horizontal axis represents the frequency and the vertical axis represents the power level. 
     According to simulation conditions, the frequency of the RF signal is 140 GHz, the frequency of the LO signal is 139 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     With reference to the graph of the IF signal, the LO-to-IF isolation will be described. When the frequency of the LO signal is 139 GHz and the magnitude of the LO signal is −10 dBm, the measurement point MPb 1  represents −70.823 dBm as a spectrum value of the IF signal. Therefore, the LO-to-IF isolation may be calculated as ‘−10-(−70.823) dBm’. That is, the LO-to-IF isolation is 60.823 dBm. 
     With reference to the graph of the RF signal, the LO-to-RF isolation will be described. When the frequency of the LO signal is 139 GHz and the magnitude of the LO signal is −10 dBm, a measurement point MPb 2  represents −72.881 dBm as a spectrum value of the RF signal. Therefore, the LO-to-RF isolation may be calculated as ‘−10-(−72.881) dBm’. That is, the LO-to-RF isolation is 62.881 dBm. 
     With reference to the graph of the LO signal, the RF-to-LO isolation will be described. When the frequency of the RF signal is 140 GHz and the magnitude of the RF signal is −30 dBm, a measurement point MPb 3  represents −62.203 dBm as a spectrum value of the LO signal. Therefore, the RF-to-LO isolation may be calculated as ‘−30-(−62.203) dBm’. That is, the RF-to-LO isolation is 32.203 dBm. 
     As described above, referring to  FIGS.  4  and  5   , the isolation of the frequency mixer  100  including the non-linear circuit  120  according to embodiments of the present disclosure may be higher than that of a frequency mixer including the general non-linear circuit NLC. That is, according to embodiments of the present disclosure, it is possible to provide a frequency mixer having improved LO-to-RF isolation, RF-to-LO isolation and LO-to-IF isolation. 
       FIG.  6    is a graph illustrating insertion loss characteristics according to some embodiments of the present disclosure. With reference to  FIG.  6   , an insertion loss of the non-linear circuit  120  and an insertion loss of the general non-linear circuit NLC according to embodiments of the present disclosure will be described. The non-linear circuit  120  may correspond to the non-linear circuit  120  of  FIG.  3   . The general non-linear circuit NLC may correspond to the general non-linear circuit NLC of  FIG.  2   . In the graph, the horizontal axis represents the frequency, and the vertical axis represents the degree of the insertion loss. 
     According to simulation conditions, the frequency range of the RF signal is 130 to 150 GHz, the frequency range of the LO signal is 129 to 149 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     Referring to the graph, the insertion loss of the frequency mixer  100  including the non-linear circuit  120  may be 12 to 20 dB. The insertion loss of a frequency mixer including the general non-linear circuit NLC may be 15 to 17 dB. 
     As described above, the insertion loss of the frequency mixer  100  including the non-linear circuit  120  according to embodiments of the present disclosure may be more uniform than the insertion loss of the frequency mixer including the general non-linear circuit NLC. 
       FIG.  7    is a graph illustrating LO-to-RF isolation according to some embodiments of the present disclosure. With reference to  FIG.  7   , the LO-to-RF isolation of the non-linear circuit  120  and LO-to-RF isolation of the general non-linear circuit NLC according to embodiments of the present disclosure will be described. The non-linear circuit  120  may correspond to the non-linear circuit  120  of  FIG.  3   . The general non-linear circuit NLC may correspond to the general non-linear circuit NLC of  FIG.  2   . In the graph, the horizontal axis represents the frequency, and the vertical axis represents the degree of isolation. 
     According to simulation conditions, the frequency range of the RF signal is 130 to 150 GHz, the frequency range of the LO signal is 129 to 149 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     Referring to the graph, the LO-to-RF isolation of the frequency mixer  100  including the non-linear circuit  120  may be 20 to 63 dB. The LO-to-RF isolation of the frequency mixer including the general non-linear circuit NLC may be 16 to 19 dB. 
     As described above, the LO-to-RF isolation of the frequency mixer  100  including the non-linear circuit  120  according to embodiments of the present disclosure may be higher than that of the frequency mixer including the general non-linear circuit NLC. 
       FIG.  8    is a graph illustrating RF-to-LO isolation in accordance with some embodiments of the present disclosure. With reference to  FIG.  8   , the RF-to-LO isolation of the non-linear circuit  120  and the RF-to-LO isolation of the general non-linear circuit NLC according to embodiments of the present disclosure will be described. The non-linear circuit  120  may correspond to the non-linear circuit  120  of  FIG.  3   . The general non-linear circuit NLC may correspond to the general non-linear circuit NLC of  FIG.  2   . In the graph, the horizontal axis represents the frequency, and the vertical axis represents the degree of isolation. 
     According to simulation conditions, the frequency range of the RF signal is 130 to 150 GHz, the frequency range of the LO signal is 129 to 149 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     Referring to the graph, the RF-to-LO isolation of the frequency mixer  100  including the non-linear circuit  120  may be 25 to 38 dB. The RF-to-LO isolation of the frequency mixer including the general non-linear circuit NLC may be 16 to 20 dB. 
     As described above, the RF-to-LO isolation of the frequency mixer  100  including the non-linear circuit  120  according to embodiments of the present disclosure may be higher than that of the frequency mixer including a general non-linear circuit (NLC). 
       FIG.  9    is a graph illustrating LO-to-IF isolation according to some embodiments of the present disclosure. With reference to  FIG.  9   , the LO-to-IF isolation of the non-linear circuit  120  and the LO-to-IF isolation of the general non-linear circuit NLC according to embodiments of the present disclosure will be described. The non-linear circuit  120  may correspond to the non-linear circuit  120  of  FIG.  3   . The general non-linear circuit NLC may correspond to the general non-linear circuit NLC of  FIG.  2   . In the graph, the horizontal axis represents the frequency, and the vertical axis represents the degree of isolation. 
     According to simulation conditions, the frequency range of the RF signal is 130 to 150 GHz, the frequency range of the LO signal is 129 to 149 GHz, and the frequency of the IF signal is 1 GHz. The magnitude of the RF signal is −30 dBm, and the magnitude of the LO signal is −10 dBm. 
     Referring to the graph, the LO-to-IF isolation of the frequency mixer  100  including the non-linear circuit  120  may be 20 to 61 dB. The LO-to-IF isolation of the frequency mixer including the general non-linear circuit NLC may be 15 to 17 dB. 
     As described above, the LO-to-IF isolation of the frequency mixer  100  including the non-linear circuit  120  according to embodiments of the present disclosure may be higher than that of the frequency mixer including the general non-linear circuit NLC. 
     According to an embodiment of the present disclosure, a frequency mixer including a non-linear circuit is provided. 
     In addition, based on the circuit structure of the non-linear circuit, a frequency mixer having improved insertion loss, linearity, and port-to-port isolation is provided. 
     While the present disclosure has been described with reference to embodiments thereof, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made thereto without departing from the spirit and scope of the present disclosure as set forth in the following claims.