JP2000091848A - Integrated mixer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for assigning ground terminals for improving the linearity of a source ground type frequency mixing circuit(mixer circuit). SOLUTION: Different terminals are assigned to the ground terminals of a local signal buffer amplifier circuit and a mixer circuit so that any influence of the pulsation of the potential of the ground terminal due to currents running through the mixer circuit side on the local signal buffer amplifier circuit can be reduced. Moreover, a resistance is added between the source and ground terminal of a pair of RF signal input MOS transistors so that any influence of the pulsation of the potential of the ground terminal can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounded source type frequency mixing circuit (mixer circuit) for a semiconductor circuit, and more particularly to an improvement in the linearity of a frequency mixing circuit using complementary field effect transistors (CMOS). The present invention relates to a mixer circuit suitable for:

[0002]

2. Description of the Related Art With the explosive spread of mobile communication, integration of high-frequency circuits used in portable terminals and the like has been actively studied. Applicable devices are Si bipolar, CM
OS (complementary field effect transistor) and so on.

As a conventional example to which a bipolar transistor is applied, for example, there is “μPC1694GR-Si-MMIC for down converter” described in pp. 1352-1379 of the NEC consumer high-frequency device data book 1993/1994. This is one in which a local oscillator, a buffer amplifier, and a mixer circuit are integrated on one chip.

FIG. 2 shows an outline of circuit connection of this conventional example. In the figure, R1 and R2 are bias resistors, R8 is a resistor for linearization, R9 and R10 are bias resistors, and Q1 and Q
2 is an RF signal input npn transistor, Q3, Q4, Q
5, Q6 are npn transistors, terminal 1 is a mixer ground terminal, terminal 2 is a mixer output terminal, terminal 3 is a mixer output terminal, terminal 7 is a mixer station oscillation signal input terminal (terminal in an integrated circuit), and terminal 8 is a mixer station. An outgoing signal input terminal (terminal in the integrated circuit), terminal pair 9 is a mixer RF signal input terminal.

[0005] The mixer circuit of FIG. 2 is a Gilbert-type multiplier in which a linearizing resistor R8 is added to the emitter. An RF (high frequency) signal is applied to the differential pair 1 to generate a differential current. This current is turned on and off by a differential pair 2 and 3 which are supplied with a large amplitude LO (local oscillation) signal and perform a switching operation.
Then, a frequency component of the difference between the RF frequency and the LO frequency and the sum is generated. By appropriately connecting a low-pass filter to the output terminal, a difference frequency component is extracted as an intermediate frequency signal.

FIG. 3 shows a block configuration of an IC using this mixer. Here, the ground potentials of all the circuits are connected to a single ground terminal, and only one of the package pins is assigned to the ground terminal. In this conventional example, all circuits of a mixer, a buffer amplifier, and a local oscillator are constituted by a differential pair circuit in which emitters are connected to each other and a connection point is connected to a current source or a resistor. Therefore, R
The F signal rarely affects the potential of the ground terminal.
This satisfies the function with one ground terminal as described herein.

In recent years, research and development of high-frequency circuits using CMOS devices, which have been applied not only to the aforementioned bipolar circuits but also to conventional logic circuits or analog and digital mixed circuits of several tens of MHz or less, have become active.
As a typical example of a mixer circuit to which a CMOS device is applied, IEEJ Journal of Solid State Circuits, Vol. 31, No. 7, pp. 880-88.
Page 9 (IEEE J of Solid-State Circuits, Vol. 31,
No. 7, July 1996), "1 GHz operation CMOS RF circuit for direct conversion receiver".

FIG. 4 shows a circuit diagram of the conventional example. In the figure, M1 and M2 are RF signal input NMOS transistors, M
3, M4, M5 and M6 are NMOS transistors, M13 to
M18 is a PMOS transistor, C1 is a capacitor, terminal 1 is a mixer ground terminal, terminal 2 is a mixer output terminal, terminal 3 is a mixer output terminal, terminal 7 is a mixer local oscillator signal input terminal (terminal in an integrated circuit), and terminal 8 is A mixer local oscillator signal input terminal (terminal in the integrated circuit), terminal pair 9 is a mixer RF signal input terminal.

This is a conventional bipolar device in which all circuits are configured using differential pairs. On the other hand, an RF (high frequency) signal input of a mixer circuit is connected to a pair of transistor pairs whose source terminals are grounded. Input to the gate. Since the source terminal is directly grounded, the current flowing through the circuit is not limited by the current source or the resistor unlike the differential pair. For this reason, when a large amplitude signal is input, a large current can flow following the input, and a circuit with high linearity can be realized.

[0010]

As described above, a mixer circuit having high linearity can be realized by utilizing the source ground circuit. However, since the source terminal is directly connected to the ground terminal, the ground terminal is used for a local oscillation signal. When the buffer amplifier is used in common, as shown in FIG. 6, when the input RF signal increases, the potential of the ground terminal inside the integrated circuit fluctuates due to the influence of the parasitic inductance L1 of the package pin. Due to this effect, the RF signal is mixed into the buffer amplifier for the local oscillation signal and the like, so that the switching operation of the mixer is incomplete and the linearity is deteriorated. As described above, in the mixer circuit in which the source of the FET is directly grounded, it is necessary to take measures against degradation of linearity due to a common impedance component attached to the ground terminal.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to provide a mixer circuit which is caused by parasitic elements and substrate conduction by separating the ground terminal of the mixer circuit and the buffer amplifier and forming both circuits on different isolated islands. This is achieved by reducing the amount of change in the potential of the ground terminal of the local signal transmitted to the local oscillation signal buffer circuit.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is shown in FIGS.
This will be described with reference to FIGS. In the figure, M1, M2
Are RF signal input NMOS transistors, M3, M4, M
5, M6 are NMOS transistors, M7 to M12 are differential pair NMOS transistors, R1 and R2 are bias resistors, R3 to R6 are load resistors, L1 is a parasitic inductor of a package and a bonding wire, C1 is a capacitor, and terminal 1 is a mixer. Terminal 2 is a mixer output terminal, terminal 3 is a mixer output terminal, terminal pair (or terminal) 4
Is a local oscillation signal buffer amplifier input terminal, a terminal 5 is a local oscillation signal buffer amplifier power supply terminal, a terminal 6 is a local oscillation signal buffer amplifier ground terminal, a terminal 7 is a mixer local oscillation signal input terminal (terminal in an integrated circuit), and a terminal 8 is A mixer local oscillator signal input terminal (terminal in the integrated circuit), terminal pair 9 is a mixer RF signal input terminal.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, different terminals (terminal 6 and terminal 1) are assigned to ground terminals of the local oscillation signal buffer amplifier circuit and the mixer circuit. As a result, it is possible to reduce the influence of the pulsation of the potential of the ground terminal caused by the current flowing on the mixer circuit side on the local buffer amplifier circuit.

The influence of the pulsation of the ground potential will be described in further detail with reference to FIGS. FIG. 5 shows the details of the buffer amplifier circuit. It is assumed that the mixer circuit and the buffer amplifier circuit shown in FIG. 5 have a common ground terminal as shown in FIG. 6, and the package and bonding wire inductances exist as a common impedance. At this time, if an RF signal is mixed into the buffer ground terminal, M11 and M12 function as a gate-grounded amplifier, undergo further impedance conversion by M7 to M10, and generate a large RF signal amplitude in load resistors R3 to R6. . Since this signal comes from the source, it is generated in phase with the load resistance pair. The large common-mode signal reduces the differential operation range of the buffer amplifier, making it impossible to obtain a differential signal sufficient for switching of the mixer. As a result, gain and linearity deteriorate.

On the other hand, in the circuit of the present invention, the effect of suppressing the LO signal by the RF signal can be reduced by separating the ground terminal of the mixer and the ground terminal of the buffer amplifier as shown in FIGS.

A second embodiment of the present invention will be described with reference to FIG. In the first embodiment, a countermeasure is taken by eliminating the common impedance of the two ground terminals by separating the ground terminals of the mixer and the buffer amplifier. However, due to the restrictions of the mounting substrate, a case where the substrate has a common impedance is assumed. In such a case, it is necessary to reduce the RF signal emitted from the mixer circuit to the ground terminal.

In FIG. 5, different terminals are assigned to ground terminals of the local oscillation signal buffer circuit and the mixer circuit. In the embodiment of FIG. 7, in order to further suppress pulsation due to an RF signal generated at the ground terminal of the mixer circuit, the resistance R
7 is added between the ground terminal and the connection point of the high frequency (RF) signal input MOS transistors M1 and M2. R7
Adds an in-phase removal effect to the M1 and M2 pairs and reduces the signal amplitude at the mixer ground terminal. According to this, M1, M
The two operating states affect each other and limit the amount of current flowing through each other, so that the linearity is slightly deteriorated. However, if the ground impedance on the substrate cannot be reduced, the next best measure is taken.

A third embodiment of the present invention will be described with reference to FIG. FIG. 8A is a top view of the semiconductor substrate, and FIG.
FIG. 8B is a cross-sectional view taken along the line AA in FIG. Silicon on insulator (Silicon
By using a substrate and arranging a local signal buffer circuit and a grounded source mixer circuit on different islands surrounded by an insulator, interference between both circuits is reduced and pulsation of the ground terminal is reduced. Becomes possible. Furthermore, by surrounding the periphery of the external extraction electrode terminal with an insulator in the same manner, the parasitic capacitance between the external extraction electrode terminal and the substrate can be reduced, and interference between signals can be reduced.

A fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a top view of a semiconductor substrate showing that a power supply contact to the substrate is separated by a local signal buffer amplifier circuit and a grounded source mixer. In this way, the ground contact is also divided by the mixer circuit and the buffer amplifier to reduce the interference between blocks.

A fifth embodiment of the present invention will be described with reference to FIG. FIG. 10 is a diagram illustrating a power supply method for the electrostatic discharge protection element. A power supply terminal to the substrate of the local oscillation signal buffer amplifier circuit and a ground terminal of the local oscillation signal buffer amplifier circuit are commonly taken out. Similarly, the power supply terminal to the substrate of the common-source mixer circuit and the common ground terminal of the common-source mixer circuit are taken out. The power supply terminal to the electrostatic discharge protection element is separated by a local signal buffer amplifier circuit and a grounded source mixer. A power supply terminal to the electrostatic discharge protection element of the local oscillation signal buffer amplifier circuit and a ground terminal of the local oscillation signal buffer amplifier circuit are commonly taken out. Similarly, the power supply terminal to the electrostatic discharge protection element of the grounded source mixer circuit and the ground terminal of the grounded source mixer circuit are commonly taken out.

This makes it possible to reduce the interference between the two circuits. According to the simulation in the 1.9 GHz band, it was confirmed that the compression point was reduced by 3 dB or more due to the influence of the parasitic capacitance of the electrostatic discharge protection element of about 0.3 pF. Is indispensable.

[0022]

According to the present invention, a 0.35 .mu.m CMOS
As a result of a circuit simulation assuming that the circuit is applied to a reception frequency mixing circuit in the MHz band, as compared with a case where the ground terminal is shared, by applying the present invention and separating the ground terminal, -1d which is an index of linearity
It was confirmed that the B compression point could be improved by 6 dB. The -1 dB compression point is defined as the input power at which the circuit performs a saturation operation and the gain is reduced by 1 dB when the input power is increased.

In the 1.9 GHz band, about 0.9
By simulation, a reduction in the compression point of 3 dB or more due to the influence of the parasitic capacitance of the electrostatic discharge protection element of 3 pF was confirmed by simulation, and it was confirmed that the separation of the substrate of the present invention and the power supply separation of the electrostatic discharge prevention element had great effects. Was.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a common-source mixer circuit according to one embodiment of the present invention.

FIG. 2 is a circuit diagram of a Gilbert multiplier using a conventional bipolar transistor.

FIG. 3 is a block diagram showing a configuration example of a conventional downconverter IC with a buffer amplifier circuit.

FIG. 4 is a circuit diagram of a conventional grounded source mixer circuit.

FIG. 5 is a circuit diagram in which details of a buffer amplifier unit of the circuit shown in FIG. 1 are added.

FIG. 6 is a block diagram showing a cause of deterioration of linearity when a common ground terminal is used in a common-source mixer circuit as in a conventional example.

FIG. 7 is a circuit diagram showing a common-source mixer circuit according to another embodiment of the present invention.

FIG. 8A is a top view and FIG. 8B is a cross-sectional view of a semiconductor substrate constituting a circuit according to one embodiment of the present invention.

FIG. 9 is a plan view showing an embodiment of a method of allocating a power supply terminal to a substrate of a common-source mixer circuit according to an embodiment of the present invention.

FIG. 10 is a block diagram showing an embodiment of a method of allocating a power supply terminal to an electrostatic discharge protection element.

[Explanation of symbols]

M1, M2: RF signal input NMOS transistor, M
3, M4, M5, M6 ... NMOS transistors, M7 to
M12: Differential pair NMOS transistor, M13 to M18
... PMOS transistors, R1, R2 ... bias resistors, R3-R6 ... load resistors, R7 ... amplitude attenuation resistors, R8
... Resistor for linearization, R9, R10 ... Bias resistor, Q1,
Q2: RF signal input npn transistor, Q3, Q4
Q5, Q6 ... npn transistor, L1 ... parasitic inductor of package and bonding wire, C1 ... capacitor, terminal 1 ... ground terminal for mixer, terminal 2 ... mixer output terminal, terminal 3 ... mixer output terminal, terminal pair 4 and terminal 4 ... Local oscillation signal buffer amplifier input terminal, terminal 5: local oscillation signal buffer amplifier power supply terminal, terminal 6: local oscillation signal buffer amplifier ground terminal, terminal 7: mixer local oscillation signal input terminal (integrated circuit terminal), terminal 8: mixer Local oscillation signal input terminal (terminal in the integrated circuit), terminal pair 9: mixer RF signal input terminal.

Claims (8)

[Claims] An amplifier circuit (a local signal buffer) for amplifying a signal amplitude of a frequency mixing circuit (mixer circuit) and a local oscillator to a predetermined size to drive the mixer circuit formed on the same semiconductor substrate. A mixer circuit and a local oscillation signal buffer circuit, wherein ground terminals of the mixer circuit and the local signal buffer circuit are separated and assigned to different terminals. 2. The integrated mixer circuit according to claim 1, wherein the sources of the first and second transistors are connected to a mixer ground terminal, and a differential signal is inputted from the gates of the first and second transistors. , Connecting the sources of the third and fourth transistors and the drain of the first transistor,
A third mixer and a fifth transistor, wherein the source of the fifth and sixth transistors is connected to the drain of the second transistor, the output terminal connecting the drains of the fourth and sixth transistors is the first mixer output terminal, A mixer circuit having an output terminal connected to the drain of the second as a second mixer output terminal, a station having an input terminal for a local oscillation signal, a power supply terminal, a ground terminal, a first buffer output terminal and a second buffer output terminal. The first buffer output terminal is connected to the gates of the fourth and fifth transistors, and the second buffer output terminal is connected to the third and fifth transistors. An integrated mixer circuit connected to the gate of a sixth transistor. 3. The integrated mixer circuit according to claim 2, wherein one end of a resistor is connected to a source terminal of the first and second signal input transistor pairs of the mixer circuit, and a terminal opposite to the resistor is connected to a ground terminal. An integrated mixer circuit characterized by being connected. 4. The integrated mixer circuit according to claim 2, wherein the first to sixth transistors are N-type conductive MOS transistors. 5. The integrated mixer circuit according to claim 2, wherein the first to sixth transistors are P-type conductive MOS transistors. 6. The integrated mixer circuit according to claim 1, wherein a silicon-on-insulator (Silicon on insulator) substrate is used as a substrate material, and a local signal buffer amplifier circuit, a source grounded mixer circuit main body, and an external extraction electrode are used. Wherein the side and bottom surfaces of each of the above are separated from each other by an insulator. 7. The integrated mixer circuit according to claim 6, wherein the separated substrate potential forming the buffer amplifier circuit is connected to the AC ground potential of the buffer amplifier, and the separated substrate potential forming the mixer circuit is connected. Is connected to an AC ground potential of the mixer circuit. 8. The integrated mixer circuit according to claim 1, wherein a ground terminal and a power supply terminal of a diode for preventing electrostatic destruction connected to an input terminal of the local oscillation signal buffer circuit are respectively connected to a ground terminal of a buffer amplifier and a power supply. An integrated mixer circuit, wherein a ground terminal of an ESD protection diode connected to a terminal of the mixer circuit is connected to a ground terminal of the mixer circuit.