JP2000357924A - Mixer circuit for low voltage and high frequency - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mixer circuit of low voltage and high frequency, which ensures the superior differential output characteristic in a simple constitution and with low noises and low power consumption by using an adder to produce the input signals, having the same amplitude and the phases opposite to each other to the 1st and 2nd differential circuits respectively. SOLUTION: A local oscillation signal LO is inputted to the base of a transistor (Tr) Q1, i.e., the non-inverted input of a 1st differential 1 (Q1, Q2), and a high frequency signal RF is inputted to the base of a Tr Q4, i.e., the non- inverted input of a 2nd differential circuit 2 (Q3, Q4). The output of an adder 5 is set so as to be (LO+RF)/2. Thus, a true input Vi1 of the circuit 1 becomes to LO-(LO+RF)/2=(LO-RF)/2, with a true input Vi2 of the circuit 2 becoming to RF-(LO+RF)/2=-(LO-RF)/2 respectively. Thereby the inputs Vi1 and Vi2 of the circuits 2 and 2 have the same amplitude and with their phases opposite to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low-voltage high-frequency mixer circuit. More specifically, the present invention relates to a low-noise, low-power-consumption high-frequency mixer used in a communication field such as a mobile phone.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a Gilbert cell double balanced mixer circuit according to the prior art. In this conventional integrated circuit mixer circuit, a high-frequency signal RF (frequency f1), which is a first input, is applied to transistors Q5 and Q6 forming a differential circuit, so that a current I5 flowing through transistor Q5 and a transistor Q6 are added. The sum of the flowing currents I6 is equal to the common emitter current Ie. Therefore, transistors Q5 and Q6 supply output currents having the same amplitude and opposite phases to the emitters of transistors Q1 and Q2 and transistors Q3 and Q4, respectively.

Two sets of differential circuits are formed by these transistors Q1 and Q2 and transistors Q3 and Q4, and a local oscillation signal LO (frequency f2) as a second input is applied to these transistors Q1 to Q4. Accordingly, the two sets of differential circuits perform the switching operation. Thus, current I5 is divided into current I1 flowing through transistor Q1 and current I2 flowing through transistor Q2, and current I6 is divided into current I3 flowing through transistor Q3 and current I4 flowing through transistor Q4. The ratio of these shunts is determined by the amplitude A2 of the second input LO.

The currents of I1-I3 and I2-I4 flow through the load resistors R1 and R2, respectively. As a result, VOUT = Vcc-R1 * (I1-I3) and VOUTX
= Vcc-R2 * (I2-I4). At this time, VOUT and VOUTX also have the same amplitude and opposite phases. Since this output voltage includes the result of multiplication of the first input and the second input, VOUT and VOUTX are equal to the first input R
It becomes a mixed signal (f1 ± f2 component) of F and the second input LO.

FIG. 8 is a circuit diagram showing an example of a mixer circuit using a differential circuit as another example of the prior art. 8 employs a first input signal LO and a second input signal RF.
Are added via resistors R1 and R2, respectively, and input to a differential circuit composed of transistors Q2 and Q3 via a transistor Q1 to obtain intermediate frequency signals VOUT and VOUTX using the differential circuit. In this configuration, only a desired intermediate frequency signal component is extracted by a resonance circuit including an LC circuit.

[0006]

However, in the mixer circuit of the Gilbert cell configuration shown in FIG. 7, since transistors are stacked vertically due to the configuration, the load is added to the emitter-collector voltage Vce of the two transistors and the load. There is a voltage drop due to resistance. The power supply voltage of a mobile phone or the like is about 3 V, and each transistor Vce cannot be increased. Regarding the characteristics of the transistor, the gain and distortion characteristics are better as Vce is larger. Therefore, in the conventional configuration in which Vce cannot be made sufficiently large, it is necessary to increase the current in order to secure gain and distortion characteristics. Therefore, there is a problem that the power consumption increases and the voltage drop due to the load resistance increases. Further, the differential circuit including the transistors Q5 and Q6 is basically an amplifying circuit, and the noise components included in the image band are mixed by the transistors Q1 to Q4. Therefore, there is a problem that the noise figure NF deteriorates.

On the other hand, in the configuration of the mixer circuit shown in FIG. 8, since the transistors are not vertically stacked, the Vce of the transistor can be sufficiently secured even at a low voltage of about 3 V, and the characteristics of the transistor can be sufficiently obtained.

However, transistor Q3, which can be regarded as a base ground, has a frequency band (R
When the F signal is about several hundred MHz), the current amplification factor hfe of the transistor is not sufficient, so that there is a problem that the differential current cannot be maintained in the current flowing through the transistors Q2 and Q3.

Also, since the circuit is basically a circuit for extracting a desired intermediate frequency from the output including distortion as a non-linear component by a resonance circuit to improve the characteristics, the output characteristics are Q (resonance of resonance) of the resonance circuit. Sharpness). If this Q is set too high, it is susceptible to the influence of temperature characteristics and the like, so a temperature compensation circuit or the like is required to obtain stable characteristics.
There is a problem that the circuit becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned prior art, and has as its object to provide a low-noise, low-power-consumption high-frequency mixer having a simple configuration and excellent differential output characteristics.

[0011]

In order to achieve the above object, the present invention comprises a first differential circuit and a second differential circuit, wherein the differential circuits have the same amplitude and opposite phases. Provided is a low-voltage high-frequency mixer circuit including an adder for generating an input signal.

According to this configuration, two sets of differential circuits are used to apply two high-frequency signals to be mixed to each of them, and based on these high-frequency signals, opposite phases with the same amplitude created by the adder are used. Input signal for mixing, the input signal conditions for each differential circuit are aligned, the differential output characteristics are improved, and the influence of the intermediate frequency signal on the output side on the high frequency signal on the input side is suppressed. In addition, the output of each differential circuit can be one differential output, and interference between signals can be reduced, so that a low-voltage high-frequency mixer circuit with good noise characteristics and low power consumption can be obtained.

In a preferred configuration example, each of the differential circuits includes:
One or a plurality of pairs of transistors having a common emitter side, one of the first and second high-frequency signals to be mixed is input to the first differential circuit, and the other is input to the second differential circuit. And the first and second high-frequency signals are input to the first and second differential circuits via the adder, and the output of the adder is the first and second high-frequency signals. Is set to の of the sum of.

According to this configuration, one of the first and second high-frequency signals to be mixed is input to each differential circuit, and a signal that is a half of the sum of the first and second high-frequency signals is input from the adder. Therefore, the differential inputs to the respective differential circuits have the same amplitude and opposite phases.

In a further preferred configuration example, the adder includes a first resistor provided between bases of a pair of transistors of the first differential circuit, and a base of the pair of transistors of the second differential circuit. And a second resistor provided therebetween.

According to this configuration, an adder can be formed with a simple configuration by using a resistor corresponding to each differential circuit.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a basic circuit diagram of a low-voltage high-frequency mixer circuit according to an embodiment of the present invention. This mixer circuit basically includes a first differential circuit 1 including a pair of transistors Q1 and Q2 having a common emitter,
Similarly, a pair of transistors Q3 and
Q2, a second differential circuit 2, and transistors Q2, Q3, which are one input terminals of these operating circuits 1, 2.
And an adder 5 connected to the base. The emitter side of the first differential circuit 1 is grounded via a constant current circuit 3 composed of, for example, a resistor, and the emitter side of the second differential circuit 2 is grounded via a constant current circuit 4 also composed of a resistance and the like. Is done. The resonance circuit 6 including the coils L1 and L2 and the capacitor C1 is connected to the collectors of the transistors Q2 and Q3 on the output sides of the first and second differential circuits 1 and 2.
Also, the transistors Q1, Q1 of the first and second differential circuits 1, 2
The power supply voltage Vcc is directly connected to the collector of Q4. This power supply voltage Vcc is a low voltage of about 3V.

In such a mixer circuit, first, the local oscillation signal LO = A1cos (2π * f1 * t) is applied to the first
To the base of the transistor Q1, which is the non-inverting input of the differential circuit 1 (Q1, Q2), and the high-frequency signal RF = A2c
os (2π * f2 * t) to the second differential circuit 2 (Q3, Q
4) is input to the base of the transistor Q4 which is the non-inverting input. A1 and A2 are LO and RF amplitudes (signal maximum values), respectively, and f1 and f2 are LO and RF, respectively.
And RF frequencies. The present invention is applicable to LO and RF, which are high-frequency signals to be mixed, at frequencies of about 100 MHz to several GHz.

Here, the output of the adder 5 is (LO + RF)
/ 2. Thus, the true input Vi1 of the first differential circuit 1 is equal to LO− (LO + RF) /
2 = (LO−RF) / 2, and the true input Vi2 of the second differential circuit 2 is RF− (LO + RF) / 2 = − (LO
-RF) / 2. Thus, the first and second
The inputs Vi1 and Vi2 of the differential circuits 1 and 2 have the same amplitude and opposite phases.

The two input signals Vi1 and Vi2 having the same amplitude and opposite phases are mixed by the two differential circuits 1 and 2 having the same configuration composed of the transistors Q1 to Q4, and provided at the non-inverting output sections of each other. LC circuit (L1, L2, C
The differential outputs VOUT and VOUTX having the same amplitude and opposite phases are output through the resonance circuit 6 of 1).

In such a circuit configuration, since a non-inverted output type differential circuit is used, the high frequency signal R which is the original input is used.
The frequency characteristics of F and the local oscillation signal LO do not deteriorate due to the Miller effect based on the parasitic capacitance between the base and the collector. Also, regarding the deterioration of differential characteristics observed at high frequencies, two sets of differential circuits are operated under the same conditions,
Since the non-inverted output of each differential circuit is used as a differential output,
Deterioration of differential characteristics can be reduced. Further, the in-phase component included in each signal is added to the transistor Q2 by the addition circuit.
Since the signal is input to the base of Q3, there is an effect that the noise can be suppressed by the differential circuit due to interference from other circuits occurring in the transmission path inside the IC.

When this output is viewed separately, it contains a distortion component generated due to nonlinearity. However, basically, the secondary component is dominant, and both VOUT and VOUTX have distortion in the same direction. Therefore, the second-order distortion component can be suppressed in the next-stage circuit by taking out the differential output. For this reason, the Q of the resonance circuit 6 can be suppressed to be low, which is more advantageous than the single output with respect to the fluctuation of the resonance frequency due to the temperature characteristic or the like. As a result, the temperature compensation circuit can be realized with a simple circuit configuration, and the degree of integration becomes a problem.
In C, a great effect is obtained.

Further, since the mixer circuit of the present invention is constituted by a non-inverting output type differential circuit, when the path that leaks from the output to the input is the first differential circuit 1 including the transistors Q1 and Q2, Q2 collector-base capacitance and base-emitter capacitance and transistor Q1
, The leakage to the input can be reduced. That is, in the configuration of the present invention, the power supply voltage Vcc is directly applied to the transistor Q constituting the input side of the differential circuit.
Since it is connected to one collector, it is possible to reduce the influence of the output signal leaking into the input signal and causing noise regardless of the parasitic capacitance of each transistor.

In the above mixer circuit of the present invention,
Since the output is taken out through the resonance circuit 6, it is possible to select a frequency, to take out an output signal with high purity, and to easily set impedance matching.

FIG. 2 is a block diagram of a low-voltage high-frequency mixer circuit showing the adder 6 of FIG. 1 more specifically. In this example, the adder 6 is composed of two resistors R1 and R2 as shown in (A), and these are added to a first resistor as shown in (B).
And the second differential circuits 1 and 2 respectively. Thus, the adder 6 can be formed with a simple configuration. In this case, the impedance needs to be kept low in order to suppress the leakage from the output to the bases of the transistors Q2 and Q3 due to the parasitic capacitance between the collector and the base, and to maintain the input differential of each differential circuit. is there.

FIG. 3 is a mixer circuit diagram according to another embodiment of the present invention. In this embodiment, a first differential circuit is constituted by a plurality of pairs (N pairs) of transistors Q1 and Q2 having a common emitter, and a plurality of pairs (N pairs) of transistors Q3 and Q4 also having a common emitter. A second differential circuit is configured. Transistors Q5 and Q6 are provided as buffer amplifiers on the input side of each differential circuit. As in the circuit of FIG. 2, the resistors R1 and R
2 is provided for each differential circuit. Also, the coils L1 and L
2 and a resonance circuit composed of a capacitor C1.

In the mixer circuit shown in FIG. 2, the intermediate frequency signals VOUT and VOUTX are prevented from leaking into the high frequency signal RF and the local oscillation signal LO via the resistors due to the use of the resistors as adders. It is necessary to keep the output impedance of the preceding stage low.

On the other hand, in the mixer circuit shown in FIG. 3, by adding the transistors Q5 and Q6 to the input section, the intermediate frequency signals VOUT and VOUTX, which are the output signals, are added to the input high-frequency signal RF and the local oscillation signal LO. It prevents leakage.

In the circuit of FIG. 2 as well, unlike the conventional mixer of the Gilbert cell configuration shown in FIG. 7, since the transistors are not stacked vertically, the collector-emitter voltage Vce of each transistor can be increased. NF is improved because the conversion efficiency is improved. However, compared to the conventional mixer circuit shown in FIG. 8, when the magnitudes of the high-frequency signal and the local oscillation signal are the same, the differential circuit has two sets of circuit configurations. Is 1/2
And NF deteriorates by about 3 dB. Therefore, in the circuit of the present embodiment, the NF is improved more than the conventional mixer by connecting the respective transistors in parallel.

FIG. 4 is a mixer circuit diagram according to still another embodiment of the present invention. In this embodiment, a local oscillation signal LO and a high-frequency signal RF are added in advance to two sets of differential circuits composed of a plurality of pairs of transistors as in FIG. The signal is input to the base of the transistor Q1 of the first differential circuit via Q7 and the capacitor C2. Second
The base of the transistor Q4 which is the input of the differential circuit of
It is grounded in an alternating current.

In the circuit of this embodiment, it is not possible to use a capacitor having an excessively large capacitance value.
Even if a signal represented by i / {1 + j2π * f * C (R1 + R2)} is input from the transistor Q4, the amplitude becomes
Vi and the above Vi / ｛1 + j2π * f * C (R1 + R
2) Since the signal having the opposite phase is 1/2 of the sum of｝ and is input to each differential circuit, an excellent differential output can be obtained without impairing the features of the present invention.

FIG. 5 is a circuit diagram showing an example of use of the low-voltage high-frequency mixer circuit according to the present invention. The mixer circuit according to the present invention relates to a low-noise and low-power-consumption high-frequency mixer used in a communication field such as a mobile phone, and includes a power supply voltage V
In each of the above embodiments, cc is a low voltage of about 3V.

As shown in FIG. 5, A for performing automatic gain control
A high-frequency signal RF whose output level is kept constant via a GC (Automatic Gain Control) circuit 8 is input to a mixer circuit 9 of the present invention, and a PLL (Phase-Locked) for synthesizing a local oscillation frequency and selecting a station or the like. Loop) The local oscillation signal LO whose phase is synchronized via the circuit 10 is input to the mixer circuit 9 and mixed as described in the above-described embodiment.
The signal is extracted as an intermediate frequency signal IF via the filter 11.

As described above, the mixer circuit according to the present invention
It is used as a mixer circuit that mixes a high-frequency signal RF and a local oscillation signal LO during reception to obtain an intermediate frequency signal IF, or a mixer circuit that converts a baseband signal into an IF signal during transmission and reception and further converts the signal to an RF frequency. In the above-described embodiment, the mixer circuit used in the receiving system is shown. However, even when the mixer circuit is used as the transmitting / receiving system, there is no difference in the configuration, operation, and operation and effect.

FIG. 6 is a configuration diagram of a balun circuit for making the output of the mixer circuit of the present invention a single output. By connecting the input terminals a and b of the balun circuit to the collectors of the transistors Q2 and Q3 of the differential circuit of each of the above-described embodiments, respectively, and providing this balun circuit in place of the above-described resonance circuit, the present invention described above. A single output can be obtained while maintaining the effect of the above.

[0036]

As described above, according to the present invention, two sets of differential circuits are to be mixed using two sets of differential circuits.
In addition to applying two high-frequency signals and adding and mixing input signals of the same amplitude and opposite phase created by the adder based on these high-frequency signals, the input signal conditions for each differential circuit are aligned and the differential The output characteristics are improved, the influence of the intermediate frequency signal on the output side on the high-frequency signal on the input side is suppressed, and the output of each differential circuit can be made one differential output, thereby reducing interference between the signals. A low-voltage high-frequency mixer circuit with good noise characteristics and low power consumption can be obtained with a reduced and simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a mixer circuit according to the present invention.

FIG. 2 is a circuit diagram of a more specific embodiment of the mixer circuit of FIG. 1;

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of still another embodiment of the present invention.

FIG. 5 is a circuit diagram of a usage example of the present invention.

FIG. 6 is a circuit diagram for obtaining a single output from the mixer circuit of the present invention.

FIG. 7 is a circuit diagram of a conventional mixer circuit.

FIG. 8 is a circuit diagram of another conventional mixer circuit.

[Explanation of symbols]

1: first differential circuit, 2: second differential circuit, 3, 4: constant current circuit, 5: adder, 6: resonance circuit, 7: adder,
8: AGC circuit, 9: mixer circuit, 10: PLL circuit,
11: Filter.

Claims (3)

[Claims] 1. A differential circuit comprising: a first differential circuit and a second differential circuit; and an adder for generating input signals having the same amplitude and opposite phases with respect to each differential circuit. Low-voltage high-frequency mixer circuit. 2. Each of the differential circuits comprises one or more pairs of transistors having a common emitter side, and one of first and second high-frequency signals to be mixed is supplied to the first differential circuit. And inputting the other to a second differential circuit, and inputting the first and second high-frequency signals to the first and second differential circuits via the adder. 2. The low-voltage high-frequency mixer circuit according to claim 1, wherein an output is set to a half of a sum of the first and second high-frequency signals. 3. The adder is provided between a base of a pair of transistors of the first differential circuit and a base of a pair of transistors of the second differential circuit. The low-voltage high-frequency mixer circuit according to claim 2, comprising a second resistor.