JP2000295043A - Frequency conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the leakage of a local signal and the higher harmonic component without largely changing circuit constitution by outputting a differential signal having a third frequency corresponding to first and second frequencies from the collectors of third and fourth transistors to which a second input signal having a second frequency at a base is differentially applied. SOLUTION: Local voltage signals SC and SD inputted to the bases of transistors Tr3 and Tr4. Since the signal complete square waves but constant through rates in rise/fall, pulse-like signal appears in the connection point ND1 of the emitters of the transistors Tr3 and Tr4 and the collector of the transistor Tr1. Thus, a wide band width signal having the period of half the input signals SC and SD to the bases of the transistors Tr3 and Tr4 and making a frequency component twice as much as the local signals SC and SD is obtained. Capacitors C1 and C2 are connected between the collectors of the transistors Tr1 and Tr2 and ground and the pulse-like signal is prevented from leaking to a base- side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit which receives two input signals having different frequencies and outputs a signal having a new frequency in accordance with the frequency of each of these input signals.

[0002]

2. Description of the Related Art In a transmission / reception circuit of a communication device, a frequency conversion circuit for generating a transmission signal or an intermediate frequency signal having a new frequency using a transmission or reception signal and a local oscillation signal (local signal) having a predetermined oscillation frequency. Is commonly used. For example, in a receiver, an intermediate frequency signal (IF signal) having a predetermined intermediate frequency is generated using the received high frequency signal (RF signal) and the local signal. Since such a frequency conversion circuit receives two input signals having different frequencies and generates an output signal having a new frequency as a difference or sum of the frequencies of these input signals, the frequency conversion circuit is usually called a mixer circuit. .

FIG. 15 shows an example of a frequency conversion circuit constituted by a Gilbert multiplication circuit. The Gilbert multiplication circuit is a circuit that outputs a multiplication signal of two input signals and is used as a multiplier, and can be applied to various uses such as an amplitude modulation circuit and a frequency conversion circuit.

[0004] As shown in the figure, this frequency conversion circuit is constituted by a double differential amplifier circuit. A differential amplifier circuit is formed by npn transistors Tr1 and Tr2. The bases of the transistors Tr1 and Tr2 are connected to the input terminals of the signals S _A and S _B , respectively. The emitters of these transistors are connected in common, and the connection point Are connected to the current source IS1. npn transistor Tr
3, Tr4 and Tr5, Tr6 each constitute a differential amplifier circuit. The bases of the transistors Tr3 and Tr6 are both connected to the input terminal of the signal S _C , and the bases of the transistors Tr4 and Tr5 are both connected to the input terminal of the signal S _D.

The emitters of the transistors Tr3 and Tr4 are connected to each other, and the connection point is connected to the collector of the transistor Tr1. Also, transistors Tr5 and T5
The emitters of r6 are connected to each other, and the connection point is connected to the collector of the transistor Tr2. The collector of the transistors Tr3 and Tr5 are connected, the connection point is connected to the supply line of the power supply voltage V _CC via a load circuit (load) L1, the collector of the transistors Tr4 and Tr6 are connected, the connection point It is connected to the supply line of the power supply voltage V _CC via the load circuit L2.

The above-mentioned Gilbert multiplication circuit comprises
Signal S_AAnd S_BIs like
Is an RF signal composed of a pair of differential signals, and the signal S_C
And S _DIs a local signal consisting of a pair of differential signals, for example.
(LO signal).

Here, the signal S_AAnd S_BDifferential RF consisting of
The differential voltage of the signal is V1 and the signal S _CAnd S_DThe difference between
The differential voltage of the dynamic LO signal is V2. Also, load circuit
Assuming that the flowing current is ΔI, the relationship shown by the following equation holds.
stand.

[0008]

(Equation 1)

In the equation (1), I _ee is a supply current of the current source IS1. V _T = kT / q, k is Boltzmann's constant, T is the temperature of the junction of the transistor, and q is the charge of electrons. At an absolute temperature of 300 ° K (27 ° Celsius), V _T = 26 mV.

If V1, V2 << (2V _T ), equation (1) can be approximated as follows.

[0011]

ΔI ≒ I _ee V1V2 / (4V _T ² ) (2)

That is, when the amplitude of the input differential signal is sufficiently small, the output signal V _OUT is approximately a product of the input signals V1 and V2. Here, for example, V1 = a ₁
sin (2πf ₁ t + φ ₁ ), V2 = a ₂ sin (2π
f ₂ t + φ ₂ ), the following equation is obtained from the equation (2).

[0013]

ΔI = I _ee a ₁ a ₂ / (4V _T ² ) sin (2πf ₁ t + φ ₁ ) sin (2πf ₂ t + φ ₂ ) = I _ee a ₁ a ₂ / (8 V _T ² ) · _{[cos (2 π (f 1} -f 2) t + φ 1 -φ 2) + cos (2 π (f 1 + f 2) t + φ 1 + φ 2)] ... (3)

From equation (3), the frequency (f ₁ −f ₂ ) component of the difference between the frequencies f ₁ and f ₂ and the sum frequency component (f
₁ + f ₂ ) are present. Usually, any one frequency component is extracted and output by the filter circuit. For example, in the receiving circuit, a signal of a frequency component of a difference between the RF signal and the local signal is extracted,
The signal is supplied to the intermediate amplifier circuit as the intermediate frequency signal IF.

Note that a local signal usually uses a rectangular wave having an amplitude sufficiently larger than 2 V _T. In this case, it has a frequency conversion function in the same manner as described above. Note that this case corresponds to the case where V2 is sufficiently large in equation (1). At this time, an approximate expression of tanh (V2 / (2V _T )) ≒ 1 is established. However, this section is always not become +1, the polarity of the differential voltage of the input terminal of the signal S _C or S _D, + or - with the code. Therefore, V1 << (2
V _T ), the above equation (1) is approximated as follows.

[0016]

ΔI = ± I _ee V1 / (2V _T ) (4)

In the equation (4), when the potential of the input terminal of the signal S _C is higher than the potential of the input terminal of the signal S _D , the sign becomes +, and conversely, the potential of the input terminal of the signal S _C becomes the signal S _D
When the potential of the input terminal is lower than the potential of the input terminal, the sign becomes-. That is, in this case, the Gilbert multiplier circuit inputs the differential R
The F signal V1 is output in proportion to a waveform obtained by inverting the polarity every half cycle of the local signal V2. In other words,
It can be considered as a multiplication of the signal I _ee V1 / (2V _T ) and the rectangular wave shown in FIG.

Here, the rectangular wave shown in FIG.
(T), and when this is Fourier series expanded, an infinite series such as the following equation is obtained.

[0019]

F (t) = (4 / π) [sin (2πf ₂ t) + (1/3) sin (6πf ₂ t) + (1/5) sin (10πf ₂ t)…]… (5 )

The result of the multiplication of I _ee V1 / (2V _T ) and f (t) includes the effects of all the terms shown in equation (5). Actually, the values other than the first term on the right side of the equation (5) become sufficiently small due to effects such as frequency characteristics of the filter circuit and the transistor. Therefore, it is sufficient to consider only the first term. By substituting V1 = a ₂ sin (2πf ₂ t + φ ₂ ), the following equation is obtained.

[0021]

I _ee (V1 / (2V _T )) f (t) = 2I _ee a ₂ / (V _T π) sin (2πf ₁ t) sin (2πf ₂ t + φ ₁ ) (6)

The function as the frequency converter can be easily understood by the calculation similar to the equation (3). The advantage of using a rectangular wave having a large amplitude as a local signal is that the amplitude of the output signal of the frequency conversion circuit increases, and as a result, the noise figure NF (Noise fi
gure) can be improved.

[0023]

By the way, in the frequency conversion circuit using the above-mentioned conventional Gilbert multiplication circuit,
The collectors of the transistors Tr1 and Tr2, ie, FIG.
At the nodes ND1 and ND2, a pulse-like voltage noise having twice the frequency of the local signal is generated. This is because an ideal rectangular wave cannot be supplied due to a limitation of a slew rate of a circuit for driving the transistors Tr3 to Tr6.
This is because the waveform has a finite time for rising and falling. Further, transistors Tr3 and Tr3
4, Tr5 and Tr6 each constitute a differential amplifier circuit, and the potential of the common emitter of the differential amplifier circuit follows the higher one of the base potentials of the two transistors constituting the differential amplifier circuit. The above-mentioned pulse-like voltage noise is generated. Figure 17 shows a transistor Tr3, Tr4 and Tr5, Tr6 base signal S _C that is input respectively, S _D waveform and pulse waveform of the noise signal S _G generated in the collector of the transistor Tr1. Since the noise signal S _H generated in the collector of the transistor Tr2 has substantially the same waveform as the noise signal S _G, the signal S _H is omitted in FIG. 17, the signal S _G
Is shown only.

Since this voltage noise appears as a pulse signal, it contains harmonic components, and the transistors Tr1 and Tr
r2, a differential signal S constituting a high-frequency RF signal
Leaks as spurious (unnecessary radiation) to the input terminal of the _A and S _B. A so-called local leak occurs. This local leak has a disadvantage of adversely affecting a circuit that outputs an RF signal.

In a normal transmitting / receiving circuit, spurious must be suppressed to a value or less specified by the Radio Law. Some recent television receivers are equipped with a plurality of tuner units so that different channels can be simultaneously received. However, since the frequency range assigned to television broadcasting is wide, if a channel assigned to a lower frequency is selected, the frequency of the local signal will also be lower, and the harmonic components of this local signal will have a higher frequency component than the channel having another higher frequency. Frequency band. For example,
When 201.15 MHz is used as the local frequency, a pulse-like noise of 402.30 MHz, which is twice the frequency, is generated. This 402.3 MHz frequency is included in the frequency range of the other channels. The same applies to the frequency of 804.60 MHz which is four times the frequency.

This pulse-like noise containing a high frequency component may adversely affect other tuner units and must be sufficiently suppressed. However, such a harmonic component having an adverse effect is several hundreds.
Since the frequency is very high, such as MHz or more, it is technically difficult to greatly attenuate the inside of the tuner unit, and there is a disadvantage that the cost increases due to the addition of components such as a filter.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a frequency conversion circuit capable of reducing leakage of a local signal and its harmonic components without largely changing a circuit configuration. It is in.

[0028]

In order to achieve the above object, a frequency conversion circuit according to the present invention has a structure in which emitters are electrically connected to each other and a first input signal having a first frequency is applied to each base. A first differential amplifier circuit including first and second transistors which are dynamically applied; a current source circuit for supplying current to the emitters of the first and second transistors; Connected and the first
Differential amplifier circuit including third and fourth transistors that are electrically connected to the collectors of the transistors and receive differentially applied second input signals having a second frequency to their bases. And the emitters are electrically connected to each other and electrically connected to the collector of the second transistor, and a second input signal having a second frequency is differentially applied to each base. A third differential amplifier circuit including fifth and sixth transistors, and electrically connected to collectors of the third and fifth transistors to which the second input signals having opposite phases are applied to respective bases; A first load circuit, and a second load circuit electrically connected to the collectors of the fourth and sixth transistors to which the second input signals having opposite phases are applied to respective bases. , The first and second transistors And first and second capacitors electrically connected between a collector of the first and second transistors and a predetermined voltage supply terminal. Is output as the differential signal having the third frequency corresponding to.

Preferably, the frequency conversion circuit according to the present invention comprises a first and a second transistor electrically connected in series between the emitter of the first transistor and the emitter of the second transistor. A resistance element is provided, and the current source circuit is electrically connected to a connection midpoint between the first and second resistance elements.

Further, the frequency conversion circuit of the present invention preferably has a resistance element electrically connected between the emitter of the first transistor and the emitter of the second transistor, and The source circuit includes a first current source that supplies a current to the emitter of the first transistor, and a second current source that supplies a current to the emitter of the second transistor.

Further, in the frequency conversion circuit of the present invention, a power supply voltage or a ground potential is preferably applied to the voltage supply terminal.

According to the present invention, in the frequency conversion circuit constituted by the differentially connected double amplifying circuits, the first
And a second input signal to which a first input signal having a frequency of
By connecting a capacitor to the collector of each of the transistors, the leakage of the second frequency component and its harmonic components contained in the second input signal to the base sides of the first and second transistors is suppressed. In addition, the capacitance value of the capacitor can be appropriately set according to the first and second frequencies, the desired intermediate frequency signal output level, and the effect of suppressing local leak. This is a small capacity that can be built in a chip, and can suppress the complexity of the circuit and the increase in area to a minimum.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a circuit diagram showing a first embodiment of the frequency conversion circuit according to the present invention. As illustrated, the frequency conversion circuit of the present embodiment is configured by a double differential amplifier circuit. A differential amplifier circuit is formed by npn transistors Tr1 and Tr2. The bases of the transistors Tr1 and Tr2 are connected to the input terminals of the signals S _A and S _B , respectively. The emitters of these transistors are connected in common, and the connection point Are connected to the current source IS1. Current source IS
1, the operating current I _ee is supplied to the differential amplifier circuit including the transistors Tr1 and Tr2. The npn transistors Tr3, Tr4 and Tr5, Tr6 each constitute a differential amplifier circuit. Transistors Tr3 and Tr6
Are connected to the input terminal of the signal S _C , and the bases of the transistors Tr4 and Tr5 are both connected to the input terminal of the signal S _D.

The emitters of the transistors Tr3 and Tr4 are connected to each other, and the connection point is connected to the collector of the transistor Tr1. Node ND by the connection point
1 is formed. Also, transistors Tr5 and Tr5
6 are connected to each other, and the connection point is connected to the collector of the transistor Tr2. A node ND2 is formed by the connection point. Capacitor C1 is connected between node ND1 and ground potential GND, and capacitor C2 is connected between node ND2 and ground potential GND.

The collectors of the transistors Tr3 and Tr5 are the same.
Connected to a load circuit (load) L1.
Supply voltage V through_CCConnected to the supply line, Transis
The collectors of the transistors Tr4 and Tr6 are connected to each other, and the connection is established.
The point is that the load circuit L2 is connected to the circuit power supply voltage V._CCConnected to the supply line
Have been. The load circuits L1 and L2 are, for example, resistors
It can be composed of children. Also, the desired frequency component
To extract only the minute, for example, the intermediate frequency f_IFrequency
To extract only the intermediate signal containing several components,
f_IA resonant circuit with a resonant frequency of
Can also.

It is composed of the above-mentioned Gilbert multiplication circuit.
Signal S_AAnd S_BIs like
Is an RF signal composed of a pair of differential signals, and the signal S_C
And S _DIs a local signal (LO) composed of a pair of differential signals.
Signal).

Hereinafter, the operation of the frequency conversion circuit of this embodiment will be described in detail using an equivalent circuit. In the frequency conversion circuit of the present embodiment shown in FIG. 1, since the circuit is symmetrical, only the left or right half circuit is used for the sake of analyzing the circuit operation. Here, for example, if only the left half circuit is taken out, the circuit shown in FIG. 2 is obtained. As shown, in this circuit, the transistors Tr3 and T
r4 forms a differential circuit, and the transistor Tr1 and the current source IS1 are equal to a current source that supplies an operating current to the differential circuit. In the bases of the transistors Tr3 and Tr4,
For example, since a local signal in the form of a differential signal is input, at a certain point in time, only one of the transistors Tr3 and Tr4 is turned on and the other is turned off. It can be simplified as follows.

In the simplified circuit shown in FIG. 3, the circuit for driving the transistor Tr3, that is, the output portion of the local signal generation circuit is constituted by a low impedance circuit such as an emitter follower, so that the transistor Tr3
Can be approximately regarded as a grounded base circuit. Further, since the output of the transistor Tr1 is output from the collector, it can be regarded as a high impedance output, that is, a current source.
Therefore, the simplified circuit of FIG. 3 can be represented by the equivalent circuit shown in FIG. However, in FIG. 4, for simplicity, the transistor Tr1 and the current source IS1 are connected to one current source IS.
It is represented by 01. In addition, since the transistor Tr3 can be approximately regarded as a grounded base circuit, its input impedance R1 is low, and it is relatively less affected by the capacitance of the capacitor C1.

As shown in FIG. 4, the transistor Tr1 and the current source IS1 are approximately represented by a current source IS01. The current I _{C is} applied to the input impedance R1 of the capacitor C1 and the transistor Tr3 connected in parallel.
And I _r flows. Further, the transistor Tr3 is therefore regarded as common base circuit, the same current as the input current I _r is supplied by a current source IS02, is inputted to the load circuit L1. An output signal _SE is generated in the load circuit L1.

Hereinafter, the capacitance value of the capacitor C1 will be considered using a mathematical expression. In the equivalent circuit of FIG. 4, when the supply current of the current source IS01 is I _O , the transistor T
current flowing through the r3 I _r, i.e., the supply current I _r of the equivalent current source IS02 is obtained by the following equation.

[0041]

[Equation 7] _{I r = (1 / R1)} I O / ((1 / R) + jωC1) = I O / (1 + jωR1C1) ... (7)

[0042] The formula (7), the absolute value of the current I _r with respect to the angular frequency omega | I _r | represents the characteristic shown in approximately 5. As illustrated, has substantially the same characteristics as the current I _r is the output signal of the equivalently low pass filter (low pass filter). Its cutoff frequency f _O , that is, the current | I
The frequency f _O when the level of _r | is attenuated by 3 dB from the maximum value is given by the following equation.

[0043]

(Equation 8)

In the frequency range higher than the cutoff frequency f _O , the level of the current | I _r | attenuates by -6 dB / Oct. Therefore, it is appropriate to use in a band lower frequency than the cut-off frequency f _O. That is, FIG.
It is appropriate to use a region having flat characteristics to the left of the roll-off point shown in FIG.

Here, in an actual circuit, the RF signal
Frequency, that is, output current I of current source IS01_OFrequency
f_OIs 170 MHz, and the output voltage of the transistor Tr3 is
Style I _rIs 2.5 mA, the output of transistor Tr3
The force impedance R1 is 10Ω according to the equation (9).
You. According to the equation (8), the capacitance value of the capacitor C1 can be calculated.
Wear. Here, C1 = 1 / (2πf_OR1) = 93.6.
pF. That is, the frequency of the RF signal is 170 MHz.
In this case, the capacitance value of the capacitor C1 becomes 99.5 pF or less.
By setting, the output is attenuated by the capacitor C1.
Current | I shown in FIG._r｜ Flat characteristics
The output is obtained in part.

[0046]

R1 ≒ 1 / gm = kT / qIc ≒ 26 (mV) / Ic (mA) (9) k: Boltzmann constant T: absolute temperature q: electron charge Ic: collector current of transistor Tr3

FIG. 6 shows an example of a frequency conversion circuit used in the simulation. As shown, this circuit has substantially the same configuration as the frequency conversion circuit of the present embodiment shown in FIG. In the differential amplifier circuit including the transistors Tr1 and Tr2, a 170 MHz oscillation signal is input to the base of the transistor Tr1 as an RF signal. On the other hand, since the base of the transistor Tr2 is grounded via the capacitor C4, an RF signal composed of a 170 MHz differential signal is equivalently input to the bases of the transistors Tr1 and Tr2.

In the simulation circuit shown in FIG. 6, a 210 MHz differential signal is used as a local signal. Further, resistance elements R11 and R12 each having a resistance value of 10Ω are used as a load circuit.

When the capacitance values of the capacitors C1 and C2 connected to the collectors of the transistors Tr1 and Tr2 are sequentially changed in the frequency conversion circuit thus configured, the simulation result shown in FIG. 7 is obtained. Here, the collector currents of the transistors Tr1 and Tr2 are I ₁ and I ₂ , respectively, and the resistance elements R11 and R12
Are output voltages V ₁ and V ₂ , respectively. FIG. 7 shows the current level of the frequency component of 170 MHz in the difference current I ₁ -I ₂ and the voltage level of the frequency component of the intermediate frequency 40 MHz in the difference voltage V ₁ -V ₂ when the capacitance values of the capacitors C1 and C2 are changed. FIG. In FIG. 7, the difference current and the difference voltage are the difference current and the difference voltage when the capacitance of the capacitors C1 and C2 is 0, that is, when the capacitors C1 and C2 are not connected to the collectors of the transistors Tr1 and Tr2. It is normalized and further expressed in dB.

As shown in FIG. 7, the frequency component of 170 MHz in the difference current I ₁ -I ₂ decreases as the capacitance value of the capacitor C1 (or C2) increases. C1 = C2
= 0, when normalized by the value of the difference current I ₁ −I ₂ ,
When C1 = C2 = 70 pF, the difference current I ₁ −I ₂
The level of the frequency component of 0 MHz is a value reduced by 3 dB. The intermediate frequency component in the difference voltage V ₁ -V ₂ obtained from the voltage signals extracted by the resistance elements R11 and R12 forming the load circuit, in this case, the frequency component of 40 MHz,
As shown in the figure, with the increase of the capacitance value of the capacitor C1 or C2, it first increases slightly (1 dB or less), but then decreases with the same tendency as the difference current I ₁ −I ₂ .

As shown in FIG. 7, by setting the capacitance values of the capacitors C1 and C2 to, for example, 70 pF or less, the current level of the output differential current I ₁ -I ₂ and the voltage of the difference voltage V ₁ -V ₂ The level is reduced by 3d as compared with the case where the capacitors C1 and C2 are not connected.
B or less.

Next, a description will be given of how the effects of pulse noise are reduced by connecting the capacitors C1 and C2. FIG. 8 shows a simplified circuit obtained by extracting only half of the frequency conversion circuit of the present embodiment shown in FIG. As illustrated, a differential amplifier circuit is configured by the transistors Tr3 and Tr4, and the transistor Tr1 and the current source IS1 function as a current source that supplies an operation current to the differential amplifier circuit.

The bases of the transistors Tr3 and Tr4 are
Voltage signals S _C and S _D shown in FIG. 9A are input as local signals. As shown in FIG.
The signals S _C and S _D are not perfect square waves, but have waveforms whose rising and falling have a constant slew rate, respectively. Therefore, the connection point between the collector of the emitter and the transistor Tr1 of the transistor Tr3 and Tr4, i.e., the node ND1, pulse signal S _G shown in (b) appears. The pulse signal S _G is signal S _C that is input to the base of the transistor Tr3 and Tr4
And half the period of S _D , the local signal 2
A signal having a wide bandwidth is obtained using the double frequency component as a fundamental wave.

[0054] Here, when the frequency of the local signal inputted to the base of the transistor Tr3 and Tr4 and f _LO, the frequency of the pulse signal S _G as described above 2f
_LO . Then, the signal S _G, integer multiples of the frequency component of 2f _LO is, as a local leak based transistors Tr1, the signal leakage. The leakage signal affects, for example, the operation of the receiver. In particular, in the case of a television receiver that receives a plurality of channels at the same time, a leaked frequency component is mixed in a received signal of another channel due to local leak, and signal degradation occurs.

In this embodiment, the transistor Tr
Capacitors C1 and C2 are respectively connected between the collectors 1 and Tr2 and the ground potential GND. These capacitors to prevent leakage to the base side of the pulse signal S _G. Hereinafter, this will be described in more detail using an equivalent circuit and mathematical formulas.

In the simplified circuit shown in FIG.
It can be seen that the transistor Tr3 forming the differential amplifier circuit is
Only one of Tr4 turns on and the other turns off
You. Therefore, FIG. 8 can be further simplified. FIG.
9 shows a circuit obtained by further simplifying the circuit shown in FIG.
As shown, this simplified circuit comprises a transistor Tr3
2 is equivalently shown when the circuit is operating.
The collector of the transistor Tr3 is connected to the load circuit L1.
The emitter is connected to the collector of the transistor Tr1.
Have been. Pulse signal S _GOf the transistor Tr1
When considering leakage to the base, the transistor Tr3
Signal S at the base of_GWill be entered
You. At this time, the collector of the transistor Tr1 and the ground
Signal is connected by the capacitor C1 connected between the ground GND.
No. S_GLeakage of the transistor Tr1 to the base
Circuit based on the equivalent circuit
Analyze using mathematical formulas.

In the simplified circuit shown in FIG. 10, the transistor Tr3 equivalently forms an emitter follower. The transistor Tr1 and the current source IS1 constitute a current source that supplies an operating current to the emitter follower. Therefore, the circuit of FIG. 10 can be represented by an equivalent circuit shown in FIG. In the equivalent circuit of FIG. 11, a resistor R2 is an output resistance of an emitter follower including a transistor Tr3.

In FIG. 11, a signal S _O is a pulse signal input to the base of the transistor Tr3. When the voltage level of the signal S _O and V _O, the voltage level V _G signal S _G appearing at node ND1 is obtained by the following equation.

[0059]

V _G = (1 / (jωC1)) V _O / (R2 + jωC1) = V _O / (1 + jωR2C1) (10)

The [0060] Equation (10), with the angular frequency ω is increased, the voltage level V _G of the pulse signal S _G appearing at the collector of the transistor Tr1 is reduced. Note that the expression (1)
Based on 0), the level of the fundamental wave and the high frequency component of the pulse signal S _G is attenuated by the size shown in approximately 12. In FIG. 12, the attenuation of the flat portion is 0 d.
B. Rolloff point in FIG. 12, for example, a voltage V _G is defined by the 3dB attenuation from the maximum value.

As shown in the figure, an angular frequency corresponding to the roll-off point (hereinafter referred to as a cut-off angular frequency for convenience)
In a frequency range lower than the omega _O, the voltage V _G is less attenuated with increasing frequency, having a substantially flat characteristic. In a frequency range higher than the cutoff frequency, decreases at the rate of voltage V _G is approximately -6 dB / Oct with increasing frequency.

Based on equation (10), the cutoff frequency f
_O is obtained as follows.

[0063]

[Equation 11]

When the frequency f _{LO of the} local signal is determined, the capacitance value of the capacitor C1 required for suppressing the local leak can be determined. Here, as an example, for example, the output impedance R2 of the emitter follower is set to 10Ω, and the frequency f _{LO of the} local signal is set to 210 MHz.
When f _LO = 420 MHz, the capacitance value of the capacitor C1 becomes _{C1 = 1 / (2πf O R2} ) = 37.9pF. That is, the collector of the transistor Tr1 and the ground potential G
By connecting the capacitor C1 of 37.9pF between ND, to a level V _G of the pulsed noise signal S _G appearing at the collectors of transistors Tr1, as compared with the case of not connecting the capacitor C1, thereby reducing about 3dB Can be. Harmonic component contained in the pulse signal S _G is also attenuated. Especially the 4f _LO component with a large level is almost 6
It is attenuated by dB.

By increasing the capacitance values of capacitors C1 and C2 connected to the collectors of transistors Tr1 and Tr2, transistors Tr1 and T2
level pulse-like noise signal S _G appearing at the collector of r2 can be further attenuate, it can be effectively prevented local leak. When the capacitance of the capacitor C1 is increased, the output level of the intermediate frequency signal IF also decreases. Therefore, it is necessary to appropriately set the capacitance values of the capacitors C1 and C2.

In the simulation described above, RF
When the frequency of the signal is 170 MHz and the frequency of the local signal is 210 MHz, capacitors C1 and C1
In order to suppress the output signal level from attenuating to 3 dB or less as compared with the case where 2 is not connected, it is necessary to set the capacitance values of the capacitors C1 and C2 to 93.6 pF or less. Under the same conditions, a local leak
In order to reduce the capacitance to 3 dB or more as compared with the case where 1 and C2 are not connected, the capacitance values of the capacitors C1 and C2 are set to 3
It must be set to 7.9 pF or more. When these are combined, the capacitance value of the capacitors C1 and C2 is set to 37.9 pF <C1 =
By setting C2 within the range of 93.6 pF, a desired intermediate frequency signal output level and a desired local attenuation characteristic can be obtained.

As described above, according to the present embodiment, a differential circuit is constituted by the transistors Tr1 and Tr2, and the first differential signal having the first frequency is input to the bases of these transistors. Transistors Tr3 and Tr
4. A differential circuit is formed by each of the transistors Tr5 and Tr6, the emitters of the transistors Tr3 and Tr4 are both connected to the collector of the transistor Tr1, and the emitters of the transistors Tr5 and Tr6 are connected to the transistor Tr2.
And a second node having a second frequency at a connection point between the bases of the transistors Tr3 and Tr6 and a connection point between the bases of the transistors Tr4 and Tr5.
Input differential signal. A connection point between the collectors of the transistors Tr3 and Tr5 and the transistors Tr4 and Tr
A signal having a third frequency based on the first and second frequencies is output from a connection point between the six collectors. Since the capacitors C1 and C2 are respectively connected between the collectors of the transistors Tr1 and Tr2 and a predetermined common potential, the level of a pulse-like noise signal generated in accordance with the second differential signal at the collectors of the transistors Tr1 and Tr2 is reduced. Thus, leakage of a noise signal to the bases of these transistors can be suppressed.

Second Embodiment FIG. 13 is a circuit diagram showing a second embodiment of the frequency conversion circuit according to the present invention. As shown in the figure, in the frequency conversion circuit of the present embodiment, except that resistance elements _RE1 and _RE2 are connected between the emitters of the transistors Tr1 and Tr2, the frequency conversion circuit of the first embodiment shown in FIG. It has almost the same configuration as the conversion circuit.

As shown in FIG. 13, the transistor Tr1
The bases of Tr2 and Tr2 are connected to input terminals of signals S _A and S _B constituting a differential signal, respectively. The resistor R _E1 is connected between the emitter of the transistor Tr1 and the node ND3, and the resistor R _E2 is connected between the emitter of the transistor Tr2 and the node ND3.
Further, the node ND3 is connected to the current source IS1. The current source IS1 supplies _ee current I to the node ND3.

As shown in the drawing, a capacitor C1 is connected between the collector of the transistor Tr1 and the ground potential GND, substantially in the same manner as in the first embodiment.
Between the collector of the capacitor C2 and the ground potential GND.
2 are connected. By appropriately setting the capacitance values of these capacitors C1 and C2, it is possible to prevent the local signal and its high frequency component from leaking to the RF signal generation side without greatly attenuating the level of the output intermediate frequency signal.

Third Embodiment FIG. 14 is a circuit diagram showing a third embodiment of the frequency conversion circuit according to the present invention. As shown, in the present embodiment,
Compared to the first embodiment shown in FIG.
The difference is that a resistor R _E3 is provided between the emitters of the transistors 1 and Tr2, and that the current sources IS11 and IS12 are connected to the emitters of the transistors Tr1 and Tr2, respectively. Other configurations are almost the same as those of the first embodiment.

As shown, the transistors Tr1 and Tr
The two bases are connected to input terminals of signals S _A and S _B constituting a differential signal, respectively. Transistor Tr1
The resistor _RE3 is connected between the emitter of the transistor Tr2. Further, the emitter of the transistor Tr1 is connected to the current source IS11, and the emitter of the transistor Tr2 is connected to the current source IS12. In the first embodiment shown in FIG. 1, the current source IS1 connected to the connection point between the emitters of the transistors Tr1 and Tr2 supplies the operating current I _ee. Sources IS11 and IS12 supply operating currents I _ee / 2 to the emitters of transistors Tr1 and Tr2, respectively.
Supply.

As described above, FIG. 13 and FIG.
According to the second and third embodiments of the present invention, the emitters of the transistors Tr1 and Tr2 constituting the differential amplifier circuit are not directly connected to each other, but are connected via a resistance element. The voltage signal generated in the resistance element connected between the emitters of these transistors becomes a negative feedback signal for the input sides of the transistors Tr1 and Tr2. This negative feedback improves the frequency characteristics and operation stability of the circuit.

In each of the above embodiments of the present invention, the other terminals of the capacitors C1 and C2 connected to the collectors of the transistors Tr1 and Tr2 are grounded. However, the present invention is not limited to this. Instead, for example, the same effect can be obtained by connecting to the power supply voltage supply line side. Further, it goes without saying that the same effect can be obtained by connecting to a low impedance reference voltage source that supplies a predetermined constant voltage other than the power supply voltage supply line and the ground line. Furthermore, in each of the above-described embodiments, the frequency conversion circuit configured with an npn transistor has been described as an example, but the present invention is not limited to this. For example, the frequency conversion circuit may be configured with a pnp transistor. it can.

[0075]

As described above, according to the frequency conversion circuit of the present invention, high-frequency pulse noise generated by a local signal by a simple change such as addition of a capacitor without complicating the circuit configuration and its noise can be obtained. There is an advantage that leakage of harmonic components can be suppressed and the performance of the circuit can be improved.
Further, according to the present invention, since the capacitance of a capacitor added to a circuit is small and an IC can be formed, an increase in circuit area can be suppressed to a necessary minimum.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a frequency conversion circuit according to the present invention.

FIG. 2 is a simplified circuit of the frequency conversion circuit of FIG.

FIG. 3 is a circuit obtained by further simplifying the circuit of FIG. 2;

FIG. 4 is an equivalent circuit of the simplified circuit shown in FIG.

FIG. 5 is a graph showing current-frequency characteristics in the equivalent circuit shown in FIG.

FIG. 6 is a circuit diagram of a simulation circuit.

FIG. 7 is a graph showing the relationship between the output level of a signal and the capacitance of a capacitor in a simulation circuit.

FIG. 8 is a circuit diagram of a simplified circuit for considering signal leakage.

FIG. 9 is a diagram showing an input signal and a pulse-like noise waveform corresponding to the input signal.

FIG. 10 is a circuit obtained by further simplifying the circuit of FIG. 8;

11 is an equivalent circuit of the simplified circuit shown in FIG.

FIG. 12 is a graph showing a relationship between signal leakage level and frequency in the equivalent circuit of FIG. 11;

FIG. 13 is a circuit diagram showing a second embodiment of the frequency conversion circuit according to the present invention.

FIG. 14 is a circuit diagram showing a third embodiment of the frequency conversion circuit according to the present invention.

FIG. 15 is a circuit diagram showing an example of a conventional frequency conversion circuit.

FIG. 16 is a diagram illustrating a local signal input to the frequency conversion circuit.

FIG. 17 is a waveform diagram showing a waveform of a local signal input to a conventional frequency conversion circuit and a pulse-like noise generated according to the local signal.

[Explanation of symbols]

Tr1, Tr2, Tr3, Tr4, Tr5, Tr6 ... transistors, C1, C2 ... capacitors, L1, L2 ... load _{circuit, R E, R E1, R} E2, R1, R2 ... resistance element, I
S1, IS2, IS3 ... current source, V _CC, V _ee ... power supply voltage, GND ... ground potential.

Claims (4)

[Claims] A first differential transistor including first and second transistors having emitters electrically connected to each other and a first input signal having a first frequency applied differentially to respective bases; A dynamic amplifier circuit, a current source circuit for supplying a current to the emitters of the first and second transistors, and an emitter electrically connected to each other and electrically connected to a collector of the first transistor, respectively. A second differential amplifier circuit including third and fourth transistors to which a second input signal having a second frequency is differentially applied to a base of the second amplifier; A third differential including fifth and sixth transistors electrically connected to the collector of the second transistor and differentially applied to each base with a second input signal having a second frequency. Dynamic amplification circuit and each base A first load circuit electrically connected to the collectors of the third and fifth transistors to which the second input signal of opposite phase is applied to the second input signal; A second load circuit electrically connected to the collectors of the fourth and sixth transistors to which the input signal is applied, and a collector connected to the collectors of the first and second transistors and a predetermined voltage supply terminal. And a first and second capacitor electrically connected between the first and second transistors, and having a third frequency corresponding to the first and second frequencies from the collectors of the third and fourth transistors. A frequency conversion circuit that outputs a differential signal. 2. An emitter of the first transistor and a second transistor.
First and second resistance elements electrically connected in series between the first and second resistance elements, and the current source circuit is electrically connected to a connection midpoint between the first and second resistance elements. The frequency conversion circuit according to claim 1, wherein the frequency conversion circuit is connected to the frequency conversion circuit. And a resistor element electrically connected between an emitter of said first transistor and an emitter of said second transistor, wherein said current source circuit is connected to an emitter of said first transistor. 2. The frequency conversion circuit according to claim 1, further comprising a first current source for supplying a current, and a second current source for supplying a current to an emitter of the second transistor. 4. The frequency conversion circuit according to claim 1, wherein a power supply voltage or a ground potential is applied to said voltage supply terminal.