Patent Publication Number: US-2023163725-A1

Title: Semiconductor device and communication device comprising the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2021-0164226 filed on Nov. 25, 2021, and priority to Korean Patent Application No. 10-2022-0063323 filed on May 24, 2022, in the Korean Intellectual Property Office, the disclosure of which are incorporated by reference in their entireties herein. 
    
    
     1. TECHNICAL FIELD 
     The present disclosure relates to a semiconductor device and a communication device comprising the same. 
     2. DISCUSSION OF RELATED ART 
     A semiconductor device may include an amplifier to increase the power of a signal. The amount of amplification provided by the amplifier is measured by its gain. All amplifiers include some form of active device. Transistor amplifiers are the most common type of amplifier. A transistor is used as the active element in a transistor amplifier. The gain of a transistor amplifier is determined by the properties of the transistor as well as the circuit the transistor is contained within. 
     Analog communication systems may include the transistor amplifier. However, when an analog communication system operates at a high speed, it may consume a large amount of power due to use of the transistor amplifier. In addition, the bandwidth of the transistor amplifier of the analog communication system needs to be increased to support a fast data transmission speed. 
     SUMMARY 
     At least one embodiment of the present disclosure provides a semiconductor device capable of operating at high speed and a communication device comprising the same. 
     According to an embodiment of the present disclosure, there is provided a semiconductor device including an amplifier configured to amplify a first input signal and a second input signal and output a first output signal and a second output signal. The amplifier includes a first amplification circuit configured to output a first amplification signal and a second amplification signal by first amplifying the first input signal and the second input signal, a second amplification circuit including a first amplification transistor turned on based on the first amplification signal to generate a first output signal, a second amplification transistor turned on based on the second amplification signal to output a second output signal, and a first bias transistor turned on based on a first bias signal to generate the first output signal, a first filter circuit including a first bias capacitor connected to the first amplification transistor and the first bias transistor to generate the first bias signal using a first bias voltage, and a common mode feedback circuit configured to receive the first and second output signals and output a feedback signal that adjusts an average of the first and second output signals to correspond to a reference signal, to the first amplifier. The first filter circuit adjusts a voltage of the first bias capacitor such that a first voltage of the first bias capacitor in a disabled state in which the amplifier does not perform an amplification operation corresponds to a second voltage of the first bias capacitor in an enabled state in which the amplifier performs the amplification operation. 
     According to an embodiment of the present disclosure, there is provided a semiconductor device comprises a first amplification circuit configured to output a first amplification signal and a second amplification signal by amplifying a first input signal and a second input signal, a second amplification circuit including a first amplification transistor turned on based on the first amplification signal to generate a first output signal, a second amplification transistor turned on based on the second amplification signal to output a second output signal, and a first bias transistor turned on based on a first bias signal to generate the first output signal, a first bias capacitor connected to the first amplification transistor and the first bias transistor, a first switch circuit configured to provide one of a bias voltage and the first amplification signal to one end of the first bias capacitor, and a common mode feedback circuit configured to receive the first and second output signals and output a feedback signal that adjusts an average of the first and second output signals to correspond to a reference signal, to the first amplifier. 
     According to an embodiment of the present disclosure, there is provided a communication device including a trans-impedance amplifier configured to amplify first and second input signals from a reception mixer, and a reception filter configured to filter an output of the trans-impedance amplifier. The trans-impedance amplifier includes a first amplification circuit configured to output a first amplification signal and a second amplification signal by amplifying the first input signal and the second input signal, a second amplification circuit including a first amplification transistor turned on based on the first amplification signal to generate a first output signal, a second amplification transistor turned on based on the second amplification signal to output a second output signal, and a first bias transistor turned on based on a first bias signal to generate the first output signal, a first filter circuit including a first bias capacitor connected to the first amplification transistor and the first bias transistor and configured to generate the first bias signal using a first bias voltage, and a common mode feedback circuit configured to receive the first and second output signals and output a feedback signal that adjusts an average of the first and second output signals to correspond to a reference signal, to the first amplifier. The first filter circuit adjusts a voltage of the first bias capacitor such that a first voltage of the first bias capacitor in a disabled state in which the amplifier does not perform an amplification operation corresponds to a second voltage of the first bias capacitor in an enabled state in which the amplifier performs the amplification operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure 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 illustrating a communication device according to an embodiment of the present disclosure; 
         FIG.  2    is a circuit diagram illustrating a trans-impedance amplifier in  FIG.  1   ; 
         FIG.  3    is a circuit diagram of the amplifier in  FIG.  2   ; 
         FIGS.  4  and  5    are diagrams explaining an operation of the amplifier according to an embodiment of the present disclosure; 
         FIGS.  6  to  8    are diagrams explaining an effect of the trans-impedance amplifier according to an embodiment of the present disclosure; and 
         FIG.  9    is a circuit diagram of an amplifier according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the attached drawings: 
       FIG.  1    is a block diagram illustrating a communication device according to an embodiment of the disclosure. 
     Referring to  FIG.  1   , a communication device  1000  may include a transceiver  1100 , a data processor  1200 , a switch  1300 , and an antenna  1400 . 
     The transceiver  1100  may include a low noise amplifier  1111 , a reception mixer  1113 , a trans-impedance amplifier (TIA)  1114 , a reception filter  1116 , a transmission filter  1121 , a trans-impedance amplifier  1122 , a transmission mixer  1124 , and a power amplifier  1125 . 
     In a reception mode, the switch  1300  may output a first reception signal Rx1 received via the antenna  1400  to the low noise amplifier  1111 . The low noise amplifier  1111  may amplify the first reception signal Rx1 to generate a second reception signal Rx2. The reception mixer  1113  may generate a third reception signal Rx3 by performing down-converting for the second reception signal Rx2. For example, the reception mixer  1113  may perform a down-converting operation on the second reception signal Rx2 to convert the second reception signal Rx2 into a lower frequency signal to generate the third reception signal Rx3. 
     The trans-impedance amplifier  1114  may generate a fourth reception signal Rx4 by amplifying the third reception signal Rx3. In an embodiment, the reception filter  1116  generates a fifth reception signal Rx5 by filtering the fourth reception signal Rx4, and may output the same signal to the data processor  1200 . 
     In an embodiment, the trans-impedance amplifier  1114  and the reception filter  1116  act to convert and filter a radio frequency (RF) current signal down-converted via the reception mixer  1113  into an intermediate frequency (IF) voltage signal. 
     In a transmission mode, the data processor  1200  may generate a first transmission signal Tx1 and output the same signal to the transceiver  1100 . The transmission filter  1121  may generate a second transmission signal Tx2 by filtering the first transmission signal Tx1, and the trans-impedance amplifier  1122  may generate a third transmission signal Tx3 by amplifying the second transmission signal Tx2. In an embodiment, the trans-impedance amplifier  1122  includes a trans-impedance amplifier. 
     The transmission mixer  1124  may generate a fourth transmission signal Tx4 by performing up-converting on the third transmission signal Tx3, and the power amplifier  1125  may amplify the fourth transmission signal Tx4 to generate a fifth transmission signal Tx5. For example, the transmission mixer  1124  may perform an up-converting operation on the third transmission signal Tx3 to convert the third transmission signal Tx3 into a higher frequency signal to generate the fourth transmission signal Tx4. The switch  1300  may connect the power amplifier  1125  to the antenna  1400 , and the fifth transmission signal Tx5 may be output to the outside via the antenna  1400 . 
       FIG.  2    is a circuit diagram illustrating the trans-impedance amplifier  1114  in  FIG.  1    according to an exemplary embodiment. 
     Referring to  FIG.  2   , the trans-impedance amplifier  1114  may include an amplifier  100  configured to receive input signals VIP and VIN, a feedback resistor RM and a feedback capacitor CM connected in parallel to an input terminal and an output terminal of the amplifier  100 . 
     Even though the configuration of the trans-impedance amplifier  1114  in  FIG.  1    will be described herein, the trans-impedance amplifier  1122  in  FIG.  1    may also include the same configuration as the configuration to be described below. 
     The input signals VIP and VIN provided to the amplifier  100  may be amplified by the amplifier  100  and may be output as output signals VOP and VON. In some embodiments, the input signals VIP and VIN may be, for example, differential signals, but the present embodiments are not limited thereto. In addition, the amplifier  100  may include an operational transmission amplifier (OTA), but the present embodiments are not limited thereto. 
     The feedback resistor RM and the feedback capacitor CM may include, for example, a variable resistor and a variable capacitor. A gain and a cutoff frequency of the trans-impedance amplifier  1114  may vary by changing a resistance level of the feedback resistor RM and/or a capacitance level of the feedback capacitor CM. For example, an additional control circuit may be present to provide a first control signal to the variable resistor to change its resistance and/or provide a second control signal to the variable capacitor to change its capacitance. 
     For example, the cutoff frequency of the trans-impedance amplifier  1114  may have characteristics that are inversely proportional to the resistance level of the feedback resistor RM and the capacitance level of the feedback capacitor CM. 
     That is, when the resistance level of the feedback resistor RM and the capacitance level of the feedback capacitor CM increase, the cutoff frequency of the trans-impedance amplifier  1114  decreases, and accordingly, the transimpedance amplifier  1114  may operate as a narrowband filter that passes an input signal with a low frequency. The narrowband filter may pass frequencies within a certain first range and reject (or attenuate) frequencies outside the first range. 
     In addition, when the resistance level of the feedback resistor RM and the capacitance level of the feedback capacitor CM decrease, the cutoff frequency of the trans-impedance amplifier  1114  increases, and accordingly, the trans-impedance amplifier  1114  may operate as a wideband filter that passes the input signal having a high frequency. The wideband filter may pass frequencies within a certain second range and reject (or attenuate) frequencies outside the second range, where the second range is larger than the first range. 
     In some embodiments, the feedback resistor RM and the feedback capacitor CM may be controlled by a digital code and be set to increase or decrease either linearly or exponentially. For example, the digital code may indicate a particular resistance value to set the feedback resistor RM or a particular capacitance level to set the feedback capacitor CM. 
       FIG.  3    is a circuit diagram of the amplifier  100  in  FIG.  2    according to an embodiment of the present disclosure. 
     Referring to  FIG.  3   , the amplifier  100  may include a first amplifier A 1  (e.g., first amplifier circuit), a second amplifier A 2  (e.g., a second amplifier circuit), a common mode feedback circuit CFC, filter circuits FC 1  and FC 2 , and switch circuits SC 1  and SC 2 . 
     The first amplifier A 1  may first amplify a first input signal VIP and a second input signal VIN to output a first amplification signal VAP and a second amplification signal VAN. 
     The first amplifier A 1  may include a bias transistor MP 3  turned on based on a bias voltage VB, a transistor MP 1  turned on based on the first input signal VIP, a transistor MP 2  turned on based on the second input signal VIN, and transistors MN 1  and MN 2  turned on based on a feedback signal VCMFB. For example, the bias voltage VB may be applied to a gate of the bias transistor MP 3 , the first input signal VIP may be applied to a gate of transistor MP 1 , the second input signal VIN may be applied to a gate of transistor MP 2 , and the feedback signal VCMFB may be applied to gates of the transistors MN 1  and MN 2 . 
     A source end of the bias transistor MP 3  may be connected to a node receiving a power supply voltage VDD, and a drain end of the bias transistor MP 3  may be connected to a source end of the transistor MP 1  and the transistor MP 2 . The bias voltage VB may be provided to a gate end (e.g., a gate or gate terminal) of the bias transistor MP 3 . The power supply voltage VDD may provide power to the amplifier  100 . The bias voltage VB may be generated by applying the power supply voltage VDD to first and second resistors. For example, the first and second transistor may form a voltage divider. In an embodiment, a magnitude of the bias voltage VB is smaller than a magnitude of the power supply voltage VDD and is larger than the magnitude of a ground voltage 
     The first input signal VIP may be provided to a gate end of the transistor MP 1 , and a drain end (e.g., a drain or drain terminal) of the transistor MP 1  may be connected to the drain end of the transistor MN 1 . The second input signal VIN may be provided to a gate end of the transistor MP 2 , and a drain end of the transistor MP 2  may be connected to a drain end of the transistor MN 2 . 
     The feedback signal VCMFB may be provided to a gate end of the transistor MN 1 , and a source end (e.g., a source or source terminal) of the transistor MN 1  may be grounded. The feedback signal VCMFB may be provided to a gate end of the transistor MN 2 , and a source end of the transistor MN 2  may be grounded. 
     In some embodiments, the bias transistor MP 3  and the transistors MP 1  and MP 2  may include a P-type transistor, and the transistors MN 1  and MN 2  may include an N-type transistor, but the present embodiment is not limited thereto. 
     The first input signal VIP may be first amplified by a bias current generated by turning on the transistor MP 1  based on the first input signal VIP and turning on the transistor MN 1  based on the feedback signal VCMFB, thus generating the first amplification signal VAP. Then, the generated first amplification signal VAP may be transmitted to a second amplifier A 2  (e.g., a gate end of a transistor MN 6 ). 
     The second input signal VIN may be first amplified by a bias current generated by turning on the transistor MP 2  based on the second input signal VIN and turning on the transistor MN 2  based on the feedback signal VCMFB, thus generating the second amplification signal VAN. Then, the generated second amplification signal VAN may be transmitted to the second amplifier A 2  (e.g., a gate end of a transistor MN 7 ). 
     In some embodiments, the first amplifier A 1  may include a miller compensation circuit MCC 3  including a resistor RB and a capacitor CB. 
     The miller compensation circuit MCC 3  may be connected between the gate ends and the drain ends of the transistors MN 1  and MN 2  to perform a compensation operation. 
     The second amplifier A 2  may second amplify the first amplification signal VAP and the second amplification signal VAN to output a first output signal VOP and a second output signal VON. 
     The second amplifier A 2  may include a bias transistor MP 6  turned on based on a first bias signal VBP, a bias transistor MP 7  turned on based on a second bias signal VBN, an amplification transistor MN 6  turned on based on the first amplification signal VAP output from the first amplifier A 1 , and an amplification transistor MN 7  turned on based on the second amplification signal VAN output from the first amplifier A 1 . The first bias signal VBP may be applied to a gate of the bias transistor MP 6 , the second bias signal VBN may be applied to a gate of the bias transistor MP 7 , the first amplification signal VAP may be applied to a gate of the amplification transistor MN 6 , and the second amplification signal VAN may be applied to a gate of the amplification transistor MN 7 . In an embodiment, the first bias signal VBP is an inverse of the second bias signal VBN. 
     The first output signal VOP may be generated by adding a bias current generated by the bias transistor MP 6  to a current generated by the amplification transistor MN 6 . That is, the first output signal VOP may be generated by the current generated by the amplification transistor MN 6  and the bias transistor MP 6 . 
     The second output signal VON may be generated by adding the bias current generated by the bias transistor MP 7  to a current generated by the amplification transistor MN 7 . That is, the second output signal VON may be generated by the current generated by the amplification transistor MN 7  and the bias transistor MP 7 . 
     A source end of the bias transistor MP 6  may be connected to the power supply voltage VDD, and a drain end of the bias transistor MP 6  may be connected to a drain end of the amplification transistor MN 6 . The gate end of the bias transistor MP 6  may be connected to a filter circuit FC 1 . 
     A source end of the bias transistor MP 7  may be connected to the power supply voltage VDD, and a drain end of the bias transistor MP 7  may be connected to a drain end of the amplification transistor MN 7 . The gate end of the bias transistor MP 7  may be connected to a filter circuit FC 2 . 
     A source end of the amplification transistor MN 6  may be grounded, and a drain end of the amplification transistor MN 6  may be connected to the drain end of the bias transistor MP 6 . The first output signal VOP may be output to the drain end of the amplification transistor MN 6 . A gate end of the amplification transistor MN 6  may be connected to the drain end of the transistor MP 1  of the first amplifier A 1  and the drain end of the transistor MN 1 . The gate end of the amplification transistor MN 6  may be connected to the filter circuit FC 1  through a switch circuit SC 1 . 
     A source end of the amplification transistor MN 7  may be grounded, and a drain end of the amplification transistor MN 7  may be connected to the drain end of the bias transistor MP 7 . The second output signal VON may be output to a drain end of the amplification transistor MN 7 . A gate end of the amplification transistor MN 7  may be connected to the drain end of the transistor MP 2  and the drain end of the transistor MN 2  of the first amplifier A 1 . The gate end of the amplification transistor MN 7  may be connected to the filter circuit FC 2  through a switch circuit SC 2 . 
     In some embodiments, bias transistors MP 7  and MP 6  may include the P-type transistor, and the amplification transistors MN 7  and MN 6  may include the N-type transistor, but the present embodiment is not limited thereto. 
     In some embodiments, the second amplifier A 2  may include a first miller compensation circuit MCC 1  and a second miller compensation circuit MCC 2  including a variable resistor RZ and a variable capacitor CC. 
     The first miller compensation circuit MCC 1  may be connected between the gate end and the drain end of the transistor MN 6  to perform a compensation operation. The second miller compensation circuit MCC 2  may be connected between the gate end and the drain end of the transistor MN 7  to perform a compensation operation. 
     In some embodiments, the amplifier  100  may include a common mode feedback circuit CFC and first and second miller compensation circuits MCC 1  and MCC 2  that perform dominant pole compensation using a miller effect. 
     The common mode feedback circuit CFC may receive the first output signal VOP and the second output signal VON, and may output the feedback signal VCMFB that adjusts an average of the first output signal VOP and the second output signal VON to correspond to a reference signal VCM. 
     In the amplifier  100 , when there is no difference between the first input signal VIP and the second input signal VIN, which are differential signals, the first output signal VOP and the second output signal VON of the amplifier  100  should be disposed at an intermediate level of an overall voltage swing. However, due to changes in power, temperature and process, and a gap between an input common mode and an output common mode of the amplifier  100 , or changes in the output common mode caused by noise, an output of the amplifier  100  may be biased to a level other than an intermediate level, leading to restriction in the operation of the amplifier  100 . 
     A common mode feedback circuit CFC may be used to prevent the output from being biased a level other than the intermedia level. The common mode feedback circuit CFC is a negative feedback circuit that detects a common mode voltage of the amplifier  100 , compares the detected common mode voltage with a reference voltage, and makes the detected common mode voltage close to the reference voltage according to the comparison results. 
     The common mode feedback circuit CFC may be used in an output terminal of the amplifier  100  to set a common mode of differential output signals. 
     The common mode feedback circuit CFC may include a bias transistor MP 8  turned on based on the bias voltage VB, a transistor MP 9  turned on based on an average of the first output signal VOP and the second output signal VON, a transistor MP 10  turned on based on the reference signal VCM, and a transistor MN 8  turned on by an output of a drain end of the transistor MP 9 , and a transistor MN 9  may be turned on by an output of a drain end of the transistor MP 10 . 
     A source end of the bias transistor MP 8  may be connected to the power supply voltage VDD, and a drain end of the bias transistor MP 8  may be connected to source ends of the transistor MP 9  and the transistor MP 10 . The bias voltage VB may be provided to a gate end of the bias transistor MP 8 . 
     An average of the first output signal VOP and the second output signal VON may be provided to a gate end of the transistor MP 9  by resistors RS and capacitors CS. The drain end of the transistor MP 9  may be connected to a drain end of the transistor MN 8 . The reference signal VCM may be provided to a gate end of the transistor MP 10 , and the drain end of the transistor MP 10  may be connected to a drain end of the transistor MN 9 . 
     A gate end of the transistor MN 8  may be connected to the drain end of the transistor MN 8 , and the feedback signal VCMFB may be output via the drain end of the transistor MN 8 . A source end of the transistor MN 8  may be grounded. A gate end of the transistor MN 9  may be connected to the drain end of the transistor MN 8 , and a source end of the transistor MN 9  may be grounded. 
     In some embodiments, the bias transistor MP 8  and the transistors MP 9  and MP 10  may include the P-type transistor, and the transistors MN 8  and MN 9  may include the N-type transistor, but the present embodiment is not limited thereto. 
     The transistors MP 9 , MP 10 , MN 8 , and MN 9  may generate the feedback signal VCMFB for adjusting the average of the first output signal VOP and the second output signal VON to correspond to the reference signal VCM. The generated feedback signal VCMFB may be provided to the first amplifier A 1 . For example, the generated feedback signal VCMFB may be provided to gate ends of the transistors MN 1  and MN 2  of the first amplifier A 1 . 
     The filter circuit FC 1  may include a resistor R 1  and a bias capacitor C 1 . In some embodiments, the filter circuit FC 1  may be a high pass filter including the resistor R 1  and the bias capacitor C 1 . The filter circuit FC 1  may generate the first bias signal VBP by using the resistor R 1  and the bias capacitor C 1 . The high pass filter passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with frequencies lower than the cutoff frequency. 
     One end of the resistor R 1  may be provided with the bias voltage VB (e.g., a first bias voltage), and the other end of the resistor R 1  may be connected to the bias capacitor C 1 . Since the bias capacitor C 1  is used such that the bias transistor MP 6  of the second amplifier A 2  generates an additional bias current, the bias capacitor C 1  may be referred to as a current reuse capacitor. In addition, since the bias capacitor C 1  is used such that the bias transistor MP 6  of the second amplifier A 2  generates an additional gain, the bias capacitor C 1  may be referred to as a gain boosting capacitor. 
     One end of the bias capacitor C 1  may be connected to the switch circuit SC 1 , and the other end of the bias capacitor C 1  may be connected to the resistor R 1 . 
     The switch circuit SC 1  may control one of a bias voltage VA (e.g., a second bias voltage) and the first amplification signal VAP to be provided to one end of the bias capacitor C 1 . That is, the switch circuit SC 1  may connect one end of the bias capacitor C 1  to either the bias voltage VA or the gate end of the amplification transistor MN 6  of the second amplifier A 2 . 
     In an embodiment, the bias voltage VA is a voltage different from the bias voltage VB. For example, the magnitude of the bias voltage VA may be greater than the magnitude of a ground voltage GND and less than the magnitude of the power supply voltage VDD, and may be simultaneously different from the magnitude of the bias voltage VB. 
     In some embodiments, the bias voltage VA may be such that a voltage of the bias capacitor C 1  in a disabled state in which the amplifier  100  fails to perform an amplification operation corresponds to the voltage of the bias capacitor C 1  in an enabled state in which the amplifier  100  performs the amplification operation. For example, the magnitude of the bias voltage VA may be determined such that a voltage difference between opposite ends of the bias capacitor C 1  when the amplifier  100  is in the disabled state is substantially the same as the voltage difference between opposite ends of the bias capacitor C 1  when the amplifier  100  is in the enabled state. 
     For example, when the power supply voltage VDD is 1.2 V, in the enabled state in which the amplifier  100  performs the amplification operation, the first bias signal VBP may be 0.8 V and the first amplification signal VAP may be 0.4 V according to characteristics of transistors or passive elements included in the amplifier  100 . In this case, the voltage difference between opposite ends of the bias capacitor C 1  in the enabled state of the amplifier  100  is 0.4 V. 
     Accordingly, in this case, the bias voltage VA may be determined to be 0.8 V. When the bias voltage VA is determined to be 0.8 V, in the disabled state in which the amplifier  100  fails to perform the amplification operation, 1.2 V of the power supply voltage VDD is applied to one end of the bias capacitor C 1 , and 0.8 V of the bias voltage VA is applied to the other end of the bias capacitor C 1 , and accordingly, in the disabled state of the amplifier  100 , the voltage difference between opposite ends of the bias capacitor C 1  may be 0.4 V. This will be described in more detail later. 
     In some embodiments, a switch circuit FC 1  may include a switch S 5  and a switch S 6 . The switch S 5  may control whether the bias voltage VA is connected to the bias capacitor C 1 , and the switch S 6  may control whether the gate end of the amplification transistor MN 6  is connected to the bias capacitor C 1 . 
     The filter circuit FC 2  may include a resistor R 2  and a bias capacitor C 2 . In an embodiment, the filter circuit FC 2  is a high pass filter including the resistor R 2  and the bias capacitor C 2 . The filter circuit FC 2  may generate the second bias signal VBN by using the resistor R 2  and the bias capacitor C 2 . 
     The bias voltage VB may be provided to one end of the resistor R 2 , and the other end of the resistor R 2  may be connected to the bias capacitor C 2 . The bias capacitor C 2  may be referred to as the current reuse capacitor or the gain boosting capacitor as described above. 
     One end of the bias capacitor C 2  may be connected to the switch circuit SC 2 , and the other end of the bias capacitor C 2  may be connected to the resistor R 2 . 
     The switch circuit SC 2  may control one of the bias voltage VA and the second amplification signal VAN to be provided to one end of the bias capacitor C 2 . That is, the switch circuit SC 2  may connect one end of the bias capacitor C 2  to either the bias voltage VA or the gate end of the amplification transistor MN 7  of the second amplifier A 2 . 
     In some embodiments, the switch circuit FC 2  may include a switch S 7  and a switch S 8 . The switch S 7  may control whether the bias voltage VA is connected to the bias capacitor C 2 , and the switch S 8  may control whether the gate end of the amplification transistor MN 7  is connected to the bias capacitor C 2 . 
     The switch S 1  may control whether the power supply voltage VDD is applied to the gate end of the bias transistor MP 6 . When the amplifier  100  is in the disabled state, the switch S 1  may be turned on to provide the power supply voltage VDD to the gate end of the bias transistor MP 6 , and when the amplifier  100  is in the enabled state, the switch S 1  may be turned off. 
     The switch S 3  may control whether the ground voltage GND is applied to the gate end of the amplification transistor MN 6 . When the amplifier  100  is in the disabled state, the switch S 3  may be turned on to provide the ground voltage GND to the gate end of the amplification transistor MN 6 , and when the amplifier  100  is in the enabled state, the switch S 3  may be turned off. 
     The switch S 2  may control whether the power supply voltage VDD is applied to the gate end of the bias transistor MP 7 . When the amplifier  100  is in the disabled state, the switch S 2  may be turned on to provide the power supply voltage VDD to the gate end of the bias transistor MP 6 , and when the amplifier  100  is in the enabled state, the switch S 2  may be turned off. 
     The switch S 4  may control whether the ground voltage GND is applied to the gate end of the amplification transistor MN 7 . When the amplifier  100  is in the disabled state, the switch S 4  is turned on to provide the ground voltage GND to the gate end of the amplification transistor MN 7 , and when the amplifier  100  is in the enabled state, the switch S 4  may be turned off. 
       FIGS.  4  and  5    are diagrams explaining an operation of the trans-impedance amplifier according to an embodiment.  FIG.  4    is a circuit diagram with the amplifier in the disabled state, and  FIG.  5    is a circuit diagram with the amplifier in the enabled state. 
     First, referring to  FIG.  4   , when the amplifier  100  is the disabled state, the switches S 1 , S 2 , S 3 , S 4 , S 5  and S 7  are turned on, and the switches S 6  and S 8  are turned off. 
     Accordingly, a voltage difference between opposite ends of the bias capacitor C 1  and the bias capacitor C 2  becomes VDD-VA. 
     Next, referring to  FIG.  5   , when the amplifier  100  is in the enabled state, the switches S 6  and S 8  are turned on, and the switches S 1 , S 2 , S 3 , S 4 , S 5 , and S 7  are turned off. 
     Accordingly, the voltage difference between opposite ends of the bias capacitor C 1  becomes VBP-VAP, and the voltage difference between opposite ends of the bias capacitor C 2  becomes VBN-VAN. Herein, the magnitudes of the first and second bias signals VBP and VBN and the first and second amplification signals VAP and VAN may vary according to design characteristics of elements included in the amplifier  100 . In the present embodiment, the magnitude of the bias voltage VA may be determined to satisfy Equation 1 below. 
     
       
         
           
             VDD - VA = VBP (VBN) - VAP (VAN) 
           
         
       
     
     The magnitude of the bias voltage VA is set as described above. When the switch circuits SC 1  and SC 2  are controlled as illustrated in  FIG.  4    in the disabled state of the amplifier  100 , and the switch circuits SC 1  and SC 2  are controlled as illustrated in  FIG.  5    in the enabled state of the amplifier  100 , even if a capacitance of the bias capacitors C 1  and C 2  is designed to be large, a high-speed operation may be performed without decreasing the start-up time of the amplifier  100 . 
     Hereinafter, this will be described in more detail with reference to  FIGS.  6  to  8   . 
       FIGS.  6  to  8    are diagrams explaining an effect of the trans-impedance amplifier according to an embodiment. 
       FIG.  6    is a circuit diagram of an amplifier  99  with a configuration different from that of the amplifier  100  described above (see  FIG.  3   ).  FIG.  7    is a circuit diagram when the amplifier in  FIG.  6    is in the disabled state, and  FIG.  8    is a circuit diagram when the amplifier in  FIG.  6    is in the enabled state. 
     Referring to  FIG.  6   , unlike the amplifier  100  described above (see  FIG.  3   ), the amplifier  99  does not include the switch circuits SC 1  and SC 2  in  FIG.  3   . 
     Since the filter circuits FC 1  and FC 2  are high-pass filters, the cutoff frequency of the high-pass filter is determined by 1/RC. Accordingly, with the increase in capacitance values of the bias capacitors C 1  and C 2 , filter linearity of the filter circuits FC 1  and FC 2  may improve even at low frequencies. Accordingly, in order to increase the performance of the filter circuits FC 1  and FC 2 , capacitance values of the bias capacitors C 1  and C 2  may need to be large. 
     However, when the capacitance values of the bias capacitors C 1  and C 2  are large, a change in the charge amount of the bias capacitors C 1  and C 2  increases when the amplifier  99  is switched from the disabled state to the enabled state. 
     For example, when the amplifier  99  is in the disabled state as illustrated in  FIG.  7   , the voltages of the bias capacitors C 1  and C 2  are VDD - GND (e.g., 1.2 V - 0 V = 1.2 V), or when the amplifier  99  is in the enabled state as illustrated in  FIG.  8   , the voltages of the bias capacitors C 1  and C 2  are changed to VBP (VBN) - VAP (VAN) (e.g., 0.8 V - 0.4 V = 0.4 V). Such voltage change is a factor that increases the start-up time of the amplifier  99  and slows the operation speed of the amplifier  99 . 
     However, when the amplifier  100  according to the present embodiment described above is in the disabled state, the voltages of the bias capacitors C 1  and C 2  are VDD-VA (for example, 1.2 V-0.8 V=0.4 V) by the switch circuits SC 1  and SC 2 . In addition, when the amplifier  100  according to the present embodiment described above is in the enabled state, the voltages of the bias capacitors C 1  and C 2  are VBP (VBN)-VAP (for example, 0.8 V-0.4 V=0.4 V). 
     That is, when the amplifier  100  is in the disabled state, the voltages of the bias capacitors C 1  and C 2  are previously adjusted (for example, charged) by the voltages of the bias capacitors C 1  and C 2  in the enabled state, thereby minimizing the amount of change in charge of the bias capacitors C 1  and C 2  when the amplifier  100  is switched from the disabled state to the enabled state. 
     Accordingly, even if the capacitance values of the bias capacitors C 1  and C 2  are designed to be large to increase performance of the filter circuits FC 1  and FC 2 , the start-up time of the amplifier  100  is not increased, and accordingly, a high-speed operation may be performed due to the short start-up time. 
       FIG.  9    is a circuit diagram of an amplifier according to an embodiment of the disclosure. 
     Hereinafter, an explanation similar to that of the above-described embodiments will be omitted and differences will be mainly described. For example, the circuit in  FIG.  9    is similar to the circuit shown in  FIG.  6   . 
     Referring to  FIG.  9   , an amplifier  101  may further include variable resistors R 11  and R 22  disposed between the power supply voltage VDD and the ground voltage GND. 
     In the present embodiment, the variable resistors R 11  and R 22  may be distribution resistors for generating the bias voltage VA. That is, the bias voltage VA may be generated by resistance values of the variable resistors R 11  and R 22 . 
     For example, when the magnitude of the power supply voltage VDD is 1.2 V and the magnitude of the bias voltage VA is 0.8 V, the ratio between the resistance value of the variable resistor R 11  and the resistance value of the variable resistor R 12  may be 1:2. A control circuit may be present providing control signals to the variable resistor R 11  and the variable resistor R 12  to set their resistance values to achieve the desired ratio such as 1:2. 
     Since the operations of the switch circuits SC 1  and SC 2  when the amplifier  101  operates in the disabled state and when the amplifier  101  operates in the enabled state are the same as those described above, redundant descriptions thereof will be omitted. 
     Exemplary embodiments of the present disclosure have been described hereinabove with reference to the accompanying drawings, but the present disclosure is not limited to the above-described exemplary embodiments, and may be implemented in various different forms. For example, one of ordinary skill in the art to which the present disclosure pertains may understand that the present disclosure may be implemented in other specific forms without changing the technical spirit of the present disclosure.