CA2323023A1 - Double balanced mixer - Google Patents
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- CA2323023A1 CA2323023A1 CA 2323023 CA2323023A CA2323023A1 CA 2323023 A1 CA2323023 A1 CA 2323023A1 CA 2323023 CA2323023 CA 2323023 CA 2323023 A CA2323023 A CA 2323023A CA 2323023 A1 CA2323023 A1 CA 2323023A1
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Abstract
A double-balanced mixer includes a first pair of differential amplifiers, in which first electrodes of the first and second transistors are connected to a current source, and a first input signal is applied to second electrodes of the first and second transistors, a second pair of differential amplifiers, in which the first electrodes of the third and fourth transistors are connected to a third electrode of the first transistor, and a second input signal is applied to the second electrode of the third and fourth transistors, a third pair of differential amplifiers, in which the first electrodes of the fifth and sixth transistors are connected to the third electrode of the second transistor, and the second input signal is applied to the second electrodes of the fifth and sixth transistors, and an impedance element provided between the first electrodes of the first and second transistors. In the double-balanced mixer, the third electrodes of the third and fifth transistors are connected, the third electrodes of the fourth and sixth transistors are connected, the current source includes a first current source and a second current source in which substantially identical currents flow, and the first electrode of the first transistor and the first electrode of the second transistor are connected to the first and second current sources, respectively.
Description
f DOUBLE-BALANCED MIXER
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a double-balanced mixer using transistors.
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a double-balanced mixer using transistors.
2. Description of the Related Art Fig. 6 shows a block diagram of a double-balanced mixer.
Differential amplifiers AMP respectively amplify a local signal Lo and a radio frequency signal RF and output the amplified signals to a mixer MIX. The mixer MIX outputs an intermediate frequency signal IF.
As the mixer MIX, a so-called Gilbert cell mixer is used and is conventionally constructed as shown in Fig. 7.
A constant current source is provided for supplying a constant current and a power supply V~~ is provided for biasing the transistors.
An oscillation-preventing resistors Re serves to improve the linearity of the mixer MIX. However, as the resistance of the resistor Re becomes higher, the conversion voltage gain drops. In order to avoid such a drop in the conversion voltage gain regardless of the increase in the resistance of Re, the resistances of output loads 3 and 4, or the current of the constant current source may be increased. However, increasing those values leads to a decrease in the saturation level of the circuit. Furthermore, in order to increase the current of the constant current source, the resistances of the resistors Re must be reduced to a very small level. When the resistances are reduced to a very small level, since the offset of the voltage drop across the resistor Re caused by slight variations of the resistance of the resistor Re becomes relatively great, the output balance of the mixer MIX is worsened.
To solve such a typical problem of the,double-balanced mixer using transistors, as disclosed in Japanese Unexamined Utility Model Application Publication No. 5-59938 or U.S.
Pat. No. 5,625,307, instead of the resistors Re shown in Fig.
7, an inductor is provided between the emitters of transistors Q1 and Q2 and the constant current source.
By providing the inductor between the constant current source and the emitters of the two transistors which are differentially connected, since the direct current bias and the alternating current can be set separately, the linearity of the input/output characteristics as well as the conversion voltage gain can be improved.
When the above-described double-balanced mixer is applied to a microwave integrated circuit, since the inductor is obtained by forming the wiring pattern thereof into, for example, a spiral shape, the area occupied by the inductor on the integrated circuit becomes great: When two inductors are provided in the integrated circuit, sufficient space is required between the two inductors so that electromagnetic coupling does not occur therebetween. This leads to a further increase in the area occupied by the inductors. In construction of the microwave integrated circuit, the number of components on a wafer has a considerable influence on the cost of the integrated circuit.
Hence, the greater the chip area, the higher the cost.
When the current of the constant current source is increased in order to increase the conversion voltage gain, the wiring width of the inductor must be increased so that the current rating of the constant current source is satisfied. As a result, the area occupied by the inductor is further increased.
Since a direct current flows through the inductor, migration may cause a short circuit within the spiral inductor or between the two inductors. In the case of the occurrence of the short circuit, the inductance of the inductor becomes less than the design inductance, which leads to variations in the electrical characteristics.
SUMMARY OF THE INVENTION ' Accordingly, it is an object of the present invention to provide a miniaturized, less expensive, and highly reliable double-balanced mixing circuit having stable characteristics by solving the foregoing problems.
To this end, there is provided a double-balanced mixer comprising: a first pair of differential amplifiers including a first and second transistors, source or emitter of the first transistor being connected to a first current source, source or emitter of the second transistor being connected to a second current source, a first input signal being inputted to gate or base of the first and second transistors, substantially the same value of currents is applied into the first and second current sources, and. an impedance element being connected between the source or emitter of the first transistor and the source or emitter of the second transistor; a second pair of differential amplifiers including a third and fourth transistors, each source or emitter of the third and fourth transistors being connected to drain or collector of the first transistor, and a second input signal being inputted to each gate or base of the third and fourth transistors; a third pair of differential amplifiers including a fifth and sixth transistors, each source or emitter of the fifth and sixth transistors being connected to drain or collector of the second transistor, and the second input signal being inputted to each gate or base of the fifth and sixth transistors; wherein drain or collector of the third transistor is connected to drain or collector of the fifth transistor, drain or collector of the fourth transistor is connected to drain or collector of the sixth transistor, and a mixed signal obtained by mixing the first input signal and the second input signal is outputted between the drain or collector of the third transistor and the drain or collector of the sixth transistor.
Since this construction allows a single impedance element to be used, the occupied area thereof is decreased.
By causing values of the currents flowing in the first and second current sources to be substantially equal, since the direct current component which flows via the impedance element can be decreased, the wiring width of the impedance element can be greatly reduced. Accordingly, the area occupied by the impedance element is further reduced.
In addition, since the direct current through the impedance element can be decreased, migration can be prevented. Accordingly, reliability of the double-balanced mixer can be improved and electrical characteristics thereof can be stabilized.
Since the direct current through the impedance element can be decreased, a direct current bias (paths of the direct current) and an alternating current signal (paths of the RF
signal) can be separately set. Therefore, since voltage feedback is applied in series to the input terminals of the radio frequency signal RF by the voltage generated between both ends of the impedance element, linearity of input/output characteristics can be improved. Accordingly, oscillation of the double-balanced mixer can be prevented.
In the double-balanced mixer, the impedance element comprises an inductor. Since the phase of the voltage-feedback applied in series across the input terminals of the radio frequency signal RF can be shifted by 90° (ninety degrees), the conversion voltage gain can be increased.
While the conversion gain is improved in the frequency band of the radio frequency signal RF, the conversion gain in the frequency band of image signal is decreased. Noise components which is converted from the image signal can be reduced without decreasing the conversion gain of the high frequency signals (radio frequency signal). Accordingly, the noise factor of the double-balanced mixer can be improved.
In the double-balanced mixer, each of the first and second current sources includes a transistor. Since the currents flowing from each of the first current source and the second current source is half the value of the current flowing from the single current source of the conventional mixer, when the first current source and the second current source are constructed using transistors, the area occupied by each current source can be halved and the circuit configuration is made without increasing the entire occupied -area.
In the double-balanced mixer, each source or emitter of the two transistors constituting the first and second current sources is commonly connected, and the two transistors are provided in adjacent regions on a semiconductor integrated circuit.
Since this construction enables the wiring efficiency of the first current source and the second current source to be increased, the area occupied by the current sources can be further decreased. Furthermore, electrical characteristics of the two current sources can be made uniform. Regardless of changes in temperature or voltage fluctuations of the power supply, since a direct current never flows through the impedance element, the wiring width of the impedance element can be considerably decreased.
Accordingly, the risk of encountering migration is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram showing the construction of a double-balanced mixer according to a first embodiment of the present invention;
Fig. 2 is a detailed circuit diagram showing the construction of an impedance element and the construction of constant current sources in the mixer shown in Fig. 1;
Fig. 3 is a graph illustrating the relationship between - $ -the frequency and the conversion gain of the double-balanced mixer shown in Fig. 2;
Fig. 4 is a detailed circuit diagram showing the construction of transistors Q7 and Q8 in the mixer shown in Fig. 2;
Fig. 5 is a circuit diagram showing the construction of a double-balanced mixer according to a second embodiment of the present invention;
Fig. 6 is a block diagram of the double-balanced mixer;
and Fig. 7 is a circuit diagram showing the construction of a conventional double-balanced mixer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows the configuration of a double-balanced mixer according to a first embodiment of the present invention.
First and second transistors Q1 and QZ constitute a first pair of differential amplifiers so that the sources of the first and second transistors Q1 and Q2 are connected to constant current sources 1 and 2, respectively. Third and fourth transistors Q3 and Q4 constitute a second pair of differential amplifiers so that the sources of the third and fourth transistors Q3 and Q4 are connected to the drain of the first transistor Q1 and so that a local signal Lo is _ g _ input to the gates of the transistors Q3 and Q4. Fifth and sixth transistors QS and Q6 constitute a third pair of differential amplifiers so that the sources of the fifth and sixth transistors QS and Q6 are connected to the drain of the second transistor QZ and so that the local signal Lo is input to the gates of the transistors Q5 and Q6. The drains of the transistors Q3 and QS are connected and the drains of the transistors Q4 and Q6 are connected. An output load 3 is provided between a power source VDD and the connection point of the drains of the transistors.Q3 and Q5, and an output load 4 is provided between the power source vDp and the connection point of the drains of the transistors Q4 and Q6.
An intermediate frequency signal IF is output between the drains of the transistors Q3 and Q6 or between the drains of the transistors Q4 and Q5.
In the double-balanced mixer, the current values of the constant current sources 1 and 2 are substantially equal and the impedance values of the output loads 3 and 4 are also substantially equal. The current values of the constant current sources 1 and 2, and the impedance values of the output loads 3 and 4 are determined such that a conversion voltage gain can be obtained in accordance with a desired output level in addition to the linearity of the input/output characteristics is ensured by an impedance circuit 5.
The local signal Lo having a level in which a limiter is activated to normal local signal level, in other words, having a level of the signal greater than that of the signal which allows square waves to be output, is inputted. The radio frequency signal RF having a level which does not cause the limiter to be activated is inputted. Therefore, in the second pair of differential amplifiers including the transistors Q3 and Q4 and the third pair of differential amplifiers including the transistors Q5 and Q6, the local signal Lo causes the transistor pair Q3 and Q5 and the transistor pair QQ and Q6 to function as a synchronous switch.
In accordance with switching operations of the synchronous switches, the radio frequency signal RF, or high frequency signal, and the local signal Lo are mixed and the mixed signal is output as the intermediate frequency signal IF.
At this time, feedback voltage is applied in series to the input terminals of the radio frequency signal RF by the voltage generated at both ends of the impedance element 5.
Because of this, since the linearity of the input/output characteristics of the mixer is improved, oscillation thereof is prevented.
Fig. 2 shows a more detailed configuration of the double-balanced mixer. In Fig. 2, an inductor L constitutes the impedance element 5 shown in Fig. 1 and transistors and Q8 constitute a part of the constant current sources 1 and 2, respectively. With this configuration voltage-feedback is applied in series to the input terminals of the radio frequency signal RF by the inductor L. Here, the voltage waveform is assumed to be a sine wave. Compared to a case in which the impedance element 5 is a resistor having an impedance which is equal to the impedance cuL of the inductor L, phase of the voltage feedback is shifted by 90 degrees. Since the amplitude ratio of the synthesized (product) waveform of two voltages whose phase difference is 90 degrees to the synthesized waveform of two voltages whose phase difference is zero is (d2)/2, the equation is expressed as 20 x log((~/2)/2) - -3 dB. Hence, the feedback value is decreased by 3 dB. This means that the conversion voltage gain is improved by 3 dB when the same linearity of input/output characteristics is obtained as in the case in which the feedback is applied using the resistor.
Fig. 3 shows the relationship between the frequency and the conversion voltage gain of the double-balanced mixer-in Fig. 2. For example, the frequency of the radio frequency signal RF which is input to the gates of the transistors Ql and Q2 is assumed to be in a range of 50 MHz to 1 GHz; the frequency of the local signal Lo which is input to the gates of the transistors Q3 to Q6 is assumed to be in the range of 1.55 GHz to 2.5 GHz; and the frequency of the intermediate signal IF which is output from the drains of the transistors Q3 to Q6 is assumed to be 1.5 GHz. At this time, an image signal having a frequency of greater than 3 GHz is also converted into the intermediate signal IF having a frequency of 1.5 GHz by the local signal Lo having a frequency of 1.55 GHz to 2.5 GHz. Since this intermediate signal IF of the image signal is regarded as a noise component, therefore it is important to suppress the conversion voltage gain of the frequency band, of the image signal.
According to Fig. 3, in comparison with the case in which the resistor is used as the impedance element 5, it~is understood that there are the following advantages in the case in which the inductor is used as the impedance circuit 5: the conversion voltage gain is improved in the range of 50 MHz to 1 GHz which is the frequency band of the radio frequency signal RF; and the conversion voltage gain is suppressed in the range of greater than 3 GHz which is a frequency band of the image signal. This is because, compared to the resistor, the impedance of the inductor is small in the frequency band of the radio frequency RF, that is, loss of the inductor itself is small. Further, the impedance of the inductor becomes large in the frequency band of the image signal. Therefore, since the noise component converted from the image signal can be reduced without decreasing the conversion gain of the radio _frequency signal RF, the noise factor of the double-balanced mixer can be improved.
Fig. 4 shows more detailed configuration of the transistors Q~ and Q8 which constitute a part of the constant current sources 1 and 2, respectively. The transistors Q~
and Q8 are configured using depletion-type FETs (Field-Effect Transistor). They are arranged in the same area on a chip so that a gate connection G is shared therebetween and the drains D1 and D2 and the sources S1 and SZ are symmetric.
The current flowing through each of the transistors Q~ and Q8 is half when compared with the case where the constant current source to which a single transistor connected is provided between a pair the differential amplifiers and the ground in a conventional manner. That is, when Idss (representing a drain current according to the gate-voltage versus drain-current characteristics of the depletion-type FET when the gate voltage is zero) of each of the FET
transistors Q~ and Qe is half of the Idss of the corresponding transistor of the conventional mixer, it is sufficient that the gate width of each of the transistors Q~
and Q8 is half of the gate width of the transistor of the conventional mixer. This causes the area occupied by each of the transistors to be halved. Accordingly, provision of the two transistors Q~ and Q8 does not lead to an increase in the overall size of the mixer. Furthermore, since the two transistors Q~ and Q8 are provided in the same area on the chip so as to be in contact with each other, the characteristics of the constant current sources l and 2 can remain uniform. Therefore, regardless of changes in temperature or changes in the voltage of the power supply, the direct current can be controlled so as not to flow through the inductor L by balancing the direct current bias.
Fig. 5 shows the construction of another double-balanced mixer. Unlike that shown in Fig. 1, the mixer is constructed using bipolar transistors. Accordingly, the local signal Lo and the radio frequency signal RF are current-input type signals. Otherwise, the double-balanced mixer in Fig. 5 functions in substantially the same manner as that shown in Fig. 1. Furthermore, the constant current sources 1 and 2 can be constructed using bipolar transistors.
In this case, by'providing bipolar transistors in the same area of the chip, the area occupied by the transistors should not be increased. In the same manner as in the constant current source described in the foregoing embodiment, the characteristics of the constant current sources remain uniform.
In the foregoing, embodiments have been described in which the two constant current sources are provided between the ground and the sources or emitters of the first pair of differential amplifiers. As long as the currents of these two current sources are balanced, the currents may be varied in accordance with changes in the power supply. This means that the two current sources are not necessarily constant current sources and mere current sources suffice for the mixer.
Differential amplifiers AMP respectively amplify a local signal Lo and a radio frequency signal RF and output the amplified signals to a mixer MIX. The mixer MIX outputs an intermediate frequency signal IF.
As the mixer MIX, a so-called Gilbert cell mixer is used and is conventionally constructed as shown in Fig. 7.
A constant current source is provided for supplying a constant current and a power supply V~~ is provided for biasing the transistors.
An oscillation-preventing resistors Re serves to improve the linearity of the mixer MIX. However, as the resistance of the resistor Re becomes higher, the conversion voltage gain drops. In order to avoid such a drop in the conversion voltage gain regardless of the increase in the resistance of Re, the resistances of output loads 3 and 4, or the current of the constant current source may be increased. However, increasing those values leads to a decrease in the saturation level of the circuit. Furthermore, in order to increase the current of the constant current source, the resistances of the resistors Re must be reduced to a very small level. When the resistances are reduced to a very small level, since the offset of the voltage drop across the resistor Re caused by slight variations of the resistance of the resistor Re becomes relatively great, the output balance of the mixer MIX is worsened.
To solve such a typical problem of the,double-balanced mixer using transistors, as disclosed in Japanese Unexamined Utility Model Application Publication No. 5-59938 or U.S.
Pat. No. 5,625,307, instead of the resistors Re shown in Fig.
7, an inductor is provided between the emitters of transistors Q1 and Q2 and the constant current source.
By providing the inductor between the constant current source and the emitters of the two transistors which are differentially connected, since the direct current bias and the alternating current can be set separately, the linearity of the input/output characteristics as well as the conversion voltage gain can be improved.
When the above-described double-balanced mixer is applied to a microwave integrated circuit, since the inductor is obtained by forming the wiring pattern thereof into, for example, a spiral shape, the area occupied by the inductor on the integrated circuit becomes great: When two inductors are provided in the integrated circuit, sufficient space is required between the two inductors so that electromagnetic coupling does not occur therebetween. This leads to a further increase in the area occupied by the inductors. In construction of the microwave integrated circuit, the number of components on a wafer has a considerable influence on the cost of the integrated circuit.
Hence, the greater the chip area, the higher the cost.
When the current of the constant current source is increased in order to increase the conversion voltage gain, the wiring width of the inductor must be increased so that the current rating of the constant current source is satisfied. As a result, the area occupied by the inductor is further increased.
Since a direct current flows through the inductor, migration may cause a short circuit within the spiral inductor or between the two inductors. In the case of the occurrence of the short circuit, the inductance of the inductor becomes less than the design inductance, which leads to variations in the electrical characteristics.
SUMMARY OF THE INVENTION ' Accordingly, it is an object of the present invention to provide a miniaturized, less expensive, and highly reliable double-balanced mixing circuit having stable characteristics by solving the foregoing problems.
To this end, there is provided a double-balanced mixer comprising: a first pair of differential amplifiers including a first and second transistors, source or emitter of the first transistor being connected to a first current source, source or emitter of the second transistor being connected to a second current source, a first input signal being inputted to gate or base of the first and second transistors, substantially the same value of currents is applied into the first and second current sources, and. an impedance element being connected between the source or emitter of the first transistor and the source or emitter of the second transistor; a second pair of differential amplifiers including a third and fourth transistors, each source or emitter of the third and fourth transistors being connected to drain or collector of the first transistor, and a second input signal being inputted to each gate or base of the third and fourth transistors; a third pair of differential amplifiers including a fifth and sixth transistors, each source or emitter of the fifth and sixth transistors being connected to drain or collector of the second transistor, and the second input signal being inputted to each gate or base of the fifth and sixth transistors; wherein drain or collector of the third transistor is connected to drain or collector of the fifth transistor, drain or collector of the fourth transistor is connected to drain or collector of the sixth transistor, and a mixed signal obtained by mixing the first input signal and the second input signal is outputted between the drain or collector of the third transistor and the drain or collector of the sixth transistor.
Since this construction allows a single impedance element to be used, the occupied area thereof is decreased.
By causing values of the currents flowing in the first and second current sources to be substantially equal, since the direct current component which flows via the impedance element can be decreased, the wiring width of the impedance element can be greatly reduced. Accordingly, the area occupied by the impedance element is further reduced.
In addition, since the direct current through the impedance element can be decreased, migration can be prevented. Accordingly, reliability of the double-balanced mixer can be improved and electrical characteristics thereof can be stabilized.
Since the direct current through the impedance element can be decreased, a direct current bias (paths of the direct current) and an alternating current signal (paths of the RF
signal) can be separately set. Therefore, since voltage feedback is applied in series to the input terminals of the radio frequency signal RF by the voltage generated between both ends of the impedance element, linearity of input/output characteristics can be improved. Accordingly, oscillation of the double-balanced mixer can be prevented.
In the double-balanced mixer, the impedance element comprises an inductor. Since the phase of the voltage-feedback applied in series across the input terminals of the radio frequency signal RF can be shifted by 90° (ninety degrees), the conversion voltage gain can be increased.
While the conversion gain is improved in the frequency band of the radio frequency signal RF, the conversion gain in the frequency band of image signal is decreased. Noise components which is converted from the image signal can be reduced without decreasing the conversion gain of the high frequency signals (radio frequency signal). Accordingly, the noise factor of the double-balanced mixer can be improved.
In the double-balanced mixer, each of the first and second current sources includes a transistor. Since the currents flowing from each of the first current source and the second current source is half the value of the current flowing from the single current source of the conventional mixer, when the first current source and the second current source are constructed using transistors, the area occupied by each current source can be halved and the circuit configuration is made without increasing the entire occupied -area.
In the double-balanced mixer, each source or emitter of the two transistors constituting the first and second current sources is commonly connected, and the two transistors are provided in adjacent regions on a semiconductor integrated circuit.
Since this construction enables the wiring efficiency of the first current source and the second current source to be increased, the area occupied by the current sources can be further decreased. Furthermore, electrical characteristics of the two current sources can be made uniform. Regardless of changes in temperature or voltage fluctuations of the power supply, since a direct current never flows through the impedance element, the wiring width of the impedance element can be considerably decreased.
Accordingly, the risk of encountering migration is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram showing the construction of a double-balanced mixer according to a first embodiment of the present invention;
Fig. 2 is a detailed circuit diagram showing the construction of an impedance element and the construction of constant current sources in the mixer shown in Fig. 1;
Fig. 3 is a graph illustrating the relationship between - $ -the frequency and the conversion gain of the double-balanced mixer shown in Fig. 2;
Fig. 4 is a detailed circuit diagram showing the construction of transistors Q7 and Q8 in the mixer shown in Fig. 2;
Fig. 5 is a circuit diagram showing the construction of a double-balanced mixer according to a second embodiment of the present invention;
Fig. 6 is a block diagram of the double-balanced mixer;
and Fig. 7 is a circuit diagram showing the construction of a conventional double-balanced mixer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows the configuration of a double-balanced mixer according to a first embodiment of the present invention.
First and second transistors Q1 and QZ constitute a first pair of differential amplifiers so that the sources of the first and second transistors Q1 and Q2 are connected to constant current sources 1 and 2, respectively. Third and fourth transistors Q3 and Q4 constitute a second pair of differential amplifiers so that the sources of the third and fourth transistors Q3 and Q4 are connected to the drain of the first transistor Q1 and so that a local signal Lo is _ g _ input to the gates of the transistors Q3 and Q4. Fifth and sixth transistors QS and Q6 constitute a third pair of differential amplifiers so that the sources of the fifth and sixth transistors QS and Q6 are connected to the drain of the second transistor QZ and so that the local signal Lo is input to the gates of the transistors Q5 and Q6. The drains of the transistors Q3 and QS are connected and the drains of the transistors Q4 and Q6 are connected. An output load 3 is provided between a power source VDD and the connection point of the drains of the transistors.Q3 and Q5, and an output load 4 is provided between the power source vDp and the connection point of the drains of the transistors Q4 and Q6.
An intermediate frequency signal IF is output between the drains of the transistors Q3 and Q6 or between the drains of the transistors Q4 and Q5.
In the double-balanced mixer, the current values of the constant current sources 1 and 2 are substantially equal and the impedance values of the output loads 3 and 4 are also substantially equal. The current values of the constant current sources 1 and 2, and the impedance values of the output loads 3 and 4 are determined such that a conversion voltage gain can be obtained in accordance with a desired output level in addition to the linearity of the input/output characteristics is ensured by an impedance circuit 5.
The local signal Lo having a level in which a limiter is activated to normal local signal level, in other words, having a level of the signal greater than that of the signal which allows square waves to be output, is inputted. The radio frequency signal RF having a level which does not cause the limiter to be activated is inputted. Therefore, in the second pair of differential amplifiers including the transistors Q3 and Q4 and the third pair of differential amplifiers including the transistors Q5 and Q6, the local signal Lo causes the transistor pair Q3 and Q5 and the transistor pair QQ and Q6 to function as a synchronous switch.
In accordance with switching operations of the synchronous switches, the radio frequency signal RF, or high frequency signal, and the local signal Lo are mixed and the mixed signal is output as the intermediate frequency signal IF.
At this time, feedback voltage is applied in series to the input terminals of the radio frequency signal RF by the voltage generated at both ends of the impedance element 5.
Because of this, since the linearity of the input/output characteristics of the mixer is improved, oscillation thereof is prevented.
Fig. 2 shows a more detailed configuration of the double-balanced mixer. In Fig. 2, an inductor L constitutes the impedance element 5 shown in Fig. 1 and transistors and Q8 constitute a part of the constant current sources 1 and 2, respectively. With this configuration voltage-feedback is applied in series to the input terminals of the radio frequency signal RF by the inductor L. Here, the voltage waveform is assumed to be a sine wave. Compared to a case in which the impedance element 5 is a resistor having an impedance which is equal to the impedance cuL of the inductor L, phase of the voltage feedback is shifted by 90 degrees. Since the amplitude ratio of the synthesized (product) waveform of two voltages whose phase difference is 90 degrees to the synthesized waveform of two voltages whose phase difference is zero is (d2)/2, the equation is expressed as 20 x log((~/2)/2) - -3 dB. Hence, the feedback value is decreased by 3 dB. This means that the conversion voltage gain is improved by 3 dB when the same linearity of input/output characteristics is obtained as in the case in which the feedback is applied using the resistor.
Fig. 3 shows the relationship between the frequency and the conversion voltage gain of the double-balanced mixer-in Fig. 2. For example, the frequency of the radio frequency signal RF which is input to the gates of the transistors Ql and Q2 is assumed to be in a range of 50 MHz to 1 GHz; the frequency of the local signal Lo which is input to the gates of the transistors Q3 to Q6 is assumed to be in the range of 1.55 GHz to 2.5 GHz; and the frequency of the intermediate signal IF which is output from the drains of the transistors Q3 to Q6 is assumed to be 1.5 GHz. At this time, an image signal having a frequency of greater than 3 GHz is also converted into the intermediate signal IF having a frequency of 1.5 GHz by the local signal Lo having a frequency of 1.55 GHz to 2.5 GHz. Since this intermediate signal IF of the image signal is regarded as a noise component, therefore it is important to suppress the conversion voltage gain of the frequency band, of the image signal.
According to Fig. 3, in comparison with the case in which the resistor is used as the impedance element 5, it~is understood that there are the following advantages in the case in which the inductor is used as the impedance circuit 5: the conversion voltage gain is improved in the range of 50 MHz to 1 GHz which is the frequency band of the radio frequency signal RF; and the conversion voltage gain is suppressed in the range of greater than 3 GHz which is a frequency band of the image signal. This is because, compared to the resistor, the impedance of the inductor is small in the frequency band of the radio frequency RF, that is, loss of the inductor itself is small. Further, the impedance of the inductor becomes large in the frequency band of the image signal. Therefore, since the noise component converted from the image signal can be reduced without decreasing the conversion gain of the radio _frequency signal RF, the noise factor of the double-balanced mixer can be improved.
Fig. 4 shows more detailed configuration of the transistors Q~ and Q8 which constitute a part of the constant current sources 1 and 2, respectively. The transistors Q~
and Q8 are configured using depletion-type FETs (Field-Effect Transistor). They are arranged in the same area on a chip so that a gate connection G is shared therebetween and the drains D1 and D2 and the sources S1 and SZ are symmetric.
The current flowing through each of the transistors Q~ and Q8 is half when compared with the case where the constant current source to which a single transistor connected is provided between a pair the differential amplifiers and the ground in a conventional manner. That is, when Idss (representing a drain current according to the gate-voltage versus drain-current characteristics of the depletion-type FET when the gate voltage is zero) of each of the FET
transistors Q~ and Qe is half of the Idss of the corresponding transistor of the conventional mixer, it is sufficient that the gate width of each of the transistors Q~
and Q8 is half of the gate width of the transistor of the conventional mixer. This causes the area occupied by each of the transistors to be halved. Accordingly, provision of the two transistors Q~ and Q8 does not lead to an increase in the overall size of the mixer. Furthermore, since the two transistors Q~ and Q8 are provided in the same area on the chip so as to be in contact with each other, the characteristics of the constant current sources l and 2 can remain uniform. Therefore, regardless of changes in temperature or changes in the voltage of the power supply, the direct current can be controlled so as not to flow through the inductor L by balancing the direct current bias.
Fig. 5 shows the construction of another double-balanced mixer. Unlike that shown in Fig. 1, the mixer is constructed using bipolar transistors. Accordingly, the local signal Lo and the radio frequency signal RF are current-input type signals. Otherwise, the double-balanced mixer in Fig. 5 functions in substantially the same manner as that shown in Fig. 1. Furthermore, the constant current sources 1 and 2 can be constructed using bipolar transistors.
In this case, by'providing bipolar transistors in the same area of the chip, the area occupied by the transistors should not be increased. In the same manner as in the constant current source described in the foregoing embodiment, the characteristics of the constant current sources remain uniform.
In the foregoing, embodiments have been described in which the two constant current sources are provided between the ground and the sources or emitters of the first pair of differential amplifiers. As long as the currents of these two current sources are balanced, the currents may be varied in accordance with changes in the power supply. This means that the two current sources are not necessarily constant current sources and mere current sources suffice for the mixer.
Claims (4)
1. A double-balanced mixer comprising:
a first pair of differential amplifiers including a first and second transistors, source or emitter of the first transistor being connected to a first current source, source or emitter of the second transistor being connected to a second current source, a first input signal being inputted to gate or base of the first and second transistors, substantially the same value of currents is applied into the first and second current sources, and an impedance element being connected between the source or emitter of the first transistor and the source or emitter of the second transistor;
a second pair of differential amplifiers including a third and fourth transistors, each source or emitter of the third and fourth transistors being connected to drain or collector of the first transistor, and a second input signal being inputted to each gate or base of the third and fourth transistors;
a third pair of differential amplifiers including a fifth and sixth transistors, each source or emitter of the fifth and sixth transistors being connected to drain or collector of the second transistor, and the second input signal being inputted to each gate or base of the fifth and sixth transistors;
wherein drain or collector of the third transistor is connected to drain or collector of the fifth transistor, drain or collector of the fourth transistor is connected to drain or collector of the sixth transistor, and a mixed signal obtained by mixing the first input signal and the second input signal is outputted between the drain or collector of the third transistor and the drain or collector of the sixth transistor.
a first pair of differential amplifiers including a first and second transistors, source or emitter of the first transistor being connected to a first current source, source or emitter of the second transistor being connected to a second current source, a first input signal being inputted to gate or base of the first and second transistors, substantially the same value of currents is applied into the first and second current sources, and an impedance element being connected between the source or emitter of the first transistor and the source or emitter of the second transistor;
a second pair of differential amplifiers including a third and fourth transistors, each source or emitter of the third and fourth transistors being connected to drain or collector of the first transistor, and a second input signal being inputted to each gate or base of the third and fourth transistors;
a third pair of differential amplifiers including a fifth and sixth transistors, each source or emitter of the fifth and sixth transistors being connected to drain or collector of the second transistor, and the second input signal being inputted to each gate or base of the fifth and sixth transistors;
wherein drain or collector of the third transistor is connected to drain or collector of the fifth transistor, drain or collector of the fourth transistor is connected to drain or collector of the sixth transistor, and a mixed signal obtained by mixing the first input signal and the second input signal is outputted between the drain or collector of the third transistor and the drain or collector of the sixth transistor.
2. A double-balanced mixer according to Claim 1, wherein said impedance element comprises an inductor.
3. A double-balanced mixer according to one of Claims 1 and 2, wherein each of the first and second current sources comprises a transistor.
4. A double-balanced mixer according to Claim 3, wherein each source or emitter of the two transistors constituting the first and second current sources is commonly connected, and the two transistors are provided in adjacent regions on a semiconductor integrated circuit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28665199A JP2001111354A (en) | 1999-10-07 | 1999-10-07 | Double balance type mixer circuit |
| JP11-286651 | 1999-10-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2323023A1 true CA2323023A1 (en) | 2001-04-07 |
Family
ID=17707195
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2323023 Abandoned CA2323023A1 (en) | 1999-10-07 | 2000-10-06 | Double balanced mixer |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2001111354A (en) |
| CA (1) | CA2323023A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116683872A (en) * | 2023-06-08 | 2023-09-01 | 上海韬润半导体有限公司 | Double-balanced mixer circuit, integrated circuit and implementation method thereof |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5001186B2 (en) * | 2008-01-31 | 2012-08-15 | 京セラ株式会社 | Multiplier circuit and communication device |
-
1999
- 1999-10-07 JP JP28665199A patent/JP2001111354A/en active Pending
-
2000
- 2000-10-06 CA CA 2323023 patent/CA2323023A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116683872A (en) * | 2023-06-08 | 2023-09-01 | 上海韬润半导体有限公司 | Double-balanced mixer circuit, integrated circuit and implementation method thereof |
| CN116683872B (en) * | 2023-06-08 | 2024-01-19 | 上海韬润半导体有限公司 | Double-balanced mixer circuit, integrated circuit and implementation method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2001111354A (en) | 2001-04-20 |
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| FZDE | Dead |