JP2737430B2 - Frequency multiplication / mixer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency multiplying / mixing circuit capable of performing a frequency multiplying operation and a mixing operation in one circuit.

[0002]

2. Description of the Related Art As is well known, when a circuit requiring both a frequency multiplying operation and a mixing operation at the same time is constructed, conventionally, for example, as shown in FIG. And the filter 43 connects between them.

[0003]

Therefore, conventionally,
It is difficult to increase the bandwidth. Further, when both circuits are integrated in a semiconductor integrated circuit, a terminal for externally attaching a filter is required, so that the number of terminals of the semiconductor integrated circuit increases.

SUMMARY OF THE INVENTION It is an object of the present invention to enable a frequency multiplying operation and a mixing operation to be performed by a single circuit, thereby eliminating the need for a filter and enabling a wide band, and suitable for a semiconductor integrated circuit. It is to provide a circuit.

[0005]

In order to achieve the above object, a frequency multiplier / mixer circuit according to the present invention has the following configuration. That is, the frequency multiplier / mixer circuit of the first invention
A first input terminal pair to which a multiplied signal is applied; a second input terminal pair to which a mixing signal is applied; and a differential pair transistor having an emitter resistance in only one of the commonly connected emitters. An amplifier composed of two sets, wherein between the two sets of differential pair transistors, the collectors of the transistors having emitter resistance and the collectors of the transistors having no emitter resistance are commonly connected to each other and have an emitter resistance. One of the bases of the transistor and the transistor having no emitter resistance is commonly connected to one input terminal of the first input terminal pair, and the other base is the other of the first input terminal pair. And the emitters of the respective differential pair transistors are connected to a constant current source. A differential amplifier having one base connected to one input terminal of the second input terminal pair and the other base connected to the other input terminal of the second input terminal pair; Second with paired transistors
And a current mirror circuit that forms a difference current from each output current of the first differential amplifier and drives the second differential amplifier based on the difference current. Things.

The frequency multiplier / mixer circuit according to a second aspect of the present invention is the frequency multiplier / mixer circuit according to the first aspect of the present invention, wherein the second differential amplifier is operated with a current obtained by subtracting a constant DC current from the difference current. A circuit for controlling the current mirror circuit as described above.

[0007]

Next, the operation of the frequency multiplying / mixing circuit of the present invention configured as described above will be described. In the present invention, the first differential amplifier forms a frequency multiplier, the second differential amplifier forms a mixer circuit, and the frequency multiplier and the mixer circuit are directly connected by a current mirror circuit. Therefore, the frequency multiplication / mixer circuit of the present invention can perform the frequency multiplication operation of the multiplied signal and the operation of mixing the frequency-multiplied signal with the mixing signal in one circuit. In addition, no external filter is required, and the bias circuit of the mixer circuit can be omitted.
The configuration is suitable for a semiconductor integrated circuit.

Further, in the second invention, the current mirror circuit is controlled so that the second differential amplifier operates with a current obtained by subtracting a constant value DC current from the difference current. In short, the constant value DC current is subtracted from the difference current between the respective output currents of the first differential amplifier as the frequency multiplier circuit, thereby operating the second differential amplifier as the mixer circuit. As a result, the drive current of the second differential amplifier is predominantly a frequency component of doubling with a very good distortion factor, and the conversion gain of the mixer circuit can be increased.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a frequency multiplier / mixer circuit according to one embodiment of the present invention. In FIG. 1, 1 and 2 are (first) input terminal pairs to which a local signal (voltage V _LO ) as a multiplied signal is applied, and 3 and 4 are to be applied with a mixing signal (voltage V _IN ) (second). ) Input terminal pair. Q1, Q2 and Q
3 and Q4 are differential pair transistors whose emitters are commonly connected, and one of the transistors (Q2, Q4)
3) only has an emitter resistor R _E. These two pairs of differential pair transistors constitute a first differential amplifier.

The collectors of the transistors having emitter resistance (Q2, Q3) and the transistors having no emitter resistance (Q1, Q4) are commonly connected between the two pairs of differential pair transistors, respectively. The bases of a transistor Q1 having no emitter resistance and a transistor Q3 having an emitter resistance are commonly connected to one input terminal 1 of the input terminal pair (1, 2), and do not have a transistor Q2 having an emitter resistance and an emitter resistance. The bases of the transistors Q4 are commonly connected to the other input terminal 2 of the input terminal pair (1, 2), and the emitters of each differential pair transistor have a constant current source I _0.
Connected to.

Next, the transistors (Q11 and Q12) are differential pair transistors constituting a second differential amplifier, and the base of the transistor Q11 has an input terminal pair (3,
4) is connected to one input terminal 3 of the transistor Q1.
2 is the other input terminal 4 of the input terminal pair (3, 4).
Connected to. And transistors (Q5 and Q6),
(Q7 and Q8) and (Q9 and Q10) constitute current mirror circuits, respectively, and directly connect both differential amplifiers. V
_CC is a power supply voltage, and _RL is a load resistance. Reference numeral 5 denotes an output terminal from which a mixer output (voltage V ₀ ) is extracted.

Hereinafter, the operation principle of this circuit will be described. In the first differential amplifier, the differential pair transistors (Q1, Q
_Assuming that the base voltages in 2) are V _B1 and V _B2 , the collector current of the transistor Q2 is I _C2 , and the current amplification factor is α _F , the following equation 1 is established.

[0013]

(Equation 1)

If V _T = kT / q (k: Boltzmann constant, T: absolute temperature, q: unit electron charge),
Since V _B1 >> V _T and V _B2 >> V _T , if I _S1 and I _S2 are the saturation currents, respectively, V _B1 , V _B2 and V _T have the relationship shown in the following Expressions 2 and 3. .

[0015]

(Equation 2)

[0016]

(Equation 3)

Assuming that I _S1 = I _S2 , Equation 1
Can be expressed as the following Expression 4.

[0018]

(Equation 4)

Further, a constant current source I ₀ and a collector current I _C1 ,
It has the relationship shown in the following Expression 5 with I _C2 .

[0020]

(Equation 5)

Therefore, Equation 4 becomes the following Equation 6.

[0022]

(Equation 6)

Therefore, the slope of the collector current I _C2 with respect to the local signal (voltage V _LO ) as the multiplied signal is obtained. That is, when differentiated, the following Expression 7 is obtained.

[0024]

(Equation 7)

Here, the point where the differential value (absolute value) becomes maximum is in the case of the following equation (8).

[0026]

(Equation 8)

Therefore, the maximum value is expressed by the following equation (9).

[0028]

(Equation 9)

At this time, the input voltage V _LO is _calculated by the following equation (10).
Becomes

[0030]

(Equation 10)

The differential pair transistors Q3 and Q4 can be similarly obtained. This can be done by reversing the polarity of the input voltage V _LO , and its derivation is omitted. Collector currents ( _IC1 , _IC2 , _IC3 , _IC4 ) of each transistor obtained as described above.
FIG. 2 shows the relationship between and the input voltage V _LO . In addition,
Figure 2 shows the case of _{R E · I 0 = 16V T} .

As can be seen from FIG. 2, the tangent at the point where the slope becomes maximum is expressed as V _{LO in} terms of the collector current I _C2.
= 4V _T as a starting point, V _LO = − (１ ／) R _E · I ₀ ,
It passes through the point of I _C2 = (１ ／) α _F · I ₀ . Where 4V
Origin of _T has become constant regardless of the value of the emitter resistor R _E and a constant current source I _0.

Then, I ₁ and I ₂ are calculated by the following equations (11) and (1).
Determined as 2.

[0034]

[Equation 11]

[0035]

(Equation 12)

Then, it can be seen that I ₁ and I ₂ are differential currents from each other, and have a double-wave rectification characteristic with respect to the input voltage V _LO . That is, if the values of the emitter resistance _RE and the constant current source are optimized, characteristics of I ₁ and I _{2 which} are substantially close to the square characteristics of the input voltage V _LO can be obtained. That is, the first differential amplifier is a frequency multiplier,
_{Since 1} and I ₂ are even functions with respect to the input voltage V _LO , it is expected that there will be little error even if the first order approximation of I ₁ and I ₂ is made up to the fourth order term of the input voltage V _LO. it can. Therefore, the difference ΔI between I ₁ and I ₂ can be approximated by the following Expression 13 using a, b, and c as constants.

[0037]

(Equation 13)

The difference ΔI is formed by two current mirror circuits (transistors (Q5, Q6) and the same (Q7, Q8)), and a current substantially equal to the difference ΔI becomes a collector current of the transistor Q8. It becomes the control current of the second current mirror circuit (the circuit of the transistors (Q9, Q10)). This third current mirror circuit is
, The collector currents of the transistors Q11 and Q12 are changed to I _C11 and I _C12.
Then, the difference between the two, that is, the output current I _OUT of the second differential amplifier is expressed by the following equation (14).

[0039]

[Equation 14]

Here, when | x | << 1, tanhx can be expanded into a series as shown in the following Expression 15.

[0041]

(Equation 15)

Therefore, when | V _IN | << 2V _T , the output current I _OUT is obtained by substituting the equation (13) and the following equation (16).
, And can be expanded as in Expression 17.

[0043]

(Equation 16)

[0044]

[Equation 17]

[0045] That is, from the formula 16 (V _LO) ² and V _IN of the product (V _LO) ² · V _IN is obtained. As a result, the output current I
_OUT has 2f _LO + f _IN , 2f _LO -f _IN or f _IN -2f
It can be seen that _LO frequency components are included. In fact, a
If << b, c << b, the frequency component becomes dominant. Accordingly, the output terminal 5 mixes the double frequency of the input signal (V _LO ) with the input signal (V _IN ) and outputs the mixed signal. This second differential amplifier is a mixer circuit.

As described above, the circuit shown in FIG. 1 can perform the frequency multiplication operation of the input signal (V _LO ) and the operation of mixing the input signal (V _IN ) with the frequency-multiplied signal in one circuit. It is. Then, the frequency multiplier circuit and the mixer circuit are directly connected by a current mirror circuit, and the output current of the frequency multiplier circuit is used as a drive current source of the mixer circuit. Therefore, the bias circuit of the mixer circuit can be omitted, and the semiconductor integrated circuit is suitable. Configuration. Of course, since an external filter is not required, a wider band can be achieved.

Next, FIG. 3 shows another embodiment of the present invention. In the second embodiment circuit, in the first embodiment circuit, a constant current source I _00, juxtaposed to the transistor Q9 of the drive source serving third current mirror circuit of the second differential amplifier, the mixer circuit The conversion gain is set to be high.
The outline will be described below.

In the third current mirror circuit, the output of the previous stage current mirror circuit (ΔI shown in the above equation 13)
The value obtained by subtracting the constant DC current value (I ₀₀ ) of the constant current source I ₀₀ from the above is used as the drive current of the second differential amplifier (mixer circuit). In the circuit of the second embodiment, the following Expression 18 is obtained.

[0049]

(Equation 18)

However, in Expression 18, the constant current sources I ₀₀ and I ₀ are related as in Expression 19 below.

[0051]

[Equation 19]

Therefore, from equation (19), since a> a ′, the output current I ₀₀ ′ of the mixer circuit can be obtained by replacing a in equation (16) and equation (17) with a ′, and calculating the following equation (20) and equation (21). Can be expressed as follows.

[0053]

(Equation 20)

[0054]

(Equation 21)

Here, since a> a ', the output current I
Ratio of Included (V _LO) ² · V _IN in ₀₀ ', from the ratio of V _IN and (V _LO) ratio of ³ is included in only the output current I ₀₀ was divided to decrease (V _LO) ² · V _IN Also increase. That is, the conversion gain of this mixer circuit could be increased. In addition,
It goes without saying that the circuit for subtracting the constant-value DC current from ΔI is not limited to the circuit shown in FIG.

[0056]

As described above, according to the frequency multiplying / mixing circuit of the present invention, the first differential amplifier forms a frequency multiplying circuit, the second differential amplifier forms a mixer circuit, Since the frequency multiplication circuit and the mixer circuit are directly connected by the current mirror circuit, the operation of multiplying the frequency of the multiplied signal and the operation of mixing the frequency-multiplied signal with the mixing signal can be performed by one circuit. That is, an external filter is not required, and the bias circuit of the mixer circuit can be omitted, so that not only the band can be widened, but also a frequency multiplier / mixer circuit suitable for semiconductor integrated circuit can be provided.

According to the second aspect of the present invention, a constant value DC current is subtracted from the difference current between the respective output currents of the first differential amplifier as a frequency multiplier, thereby operating the second differential amplifier as a mixer circuit. There is an effect that the conversion gain of the mixer circuit can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a frequency multiplier / mixer circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a frequency multiplier.

FIG. 3 is a circuit diagram of a frequency multiplier / mixer circuit according to another embodiment of the present invention.

FIG. 4 shows a conventional configuration example in which a frequency multiplying operation and a mixing operation are simultaneously required.

[Explanation of symbols]

Reference Signs List 1 input terminal 2 input terminal 3 input terminal 4 input terminal 5 output terminal Q1 to Q15 Transistor I ₀ constant current source I ₀₀ constant current source

Claims (2)

(57) [Claims] A first input terminal pair to which a multiplied signal is applied; a second input terminal pair to which a mixing signal is applied; only one of the commonly connected emitters has an emitter resistance. An amplifier comprising two pairs of differential pair transistors, wherein between the two pairs of differential pair transistors, collectors of transistors having emitter resistance and collectors of transistors having no emitter resistance are commonly connected. One of the bases of the transistor having the emitter resistance and the transistor having no emitter resistance is commonly connected to one input terminal of the first input terminal pair, and the other base is connected to the first input terminal. A common current source is connected to the other input terminal of the input terminal pair, and the emitters of the respective differential pair transistors are connected to a constant current source. A first differential amplifier connected; one base connected to one input terminal of the second input terminal pair, and the other base connected to the other input terminal of the second input terminal pair; A second differential amplifier comprising a differential pair transistor; and a current mirror for forming a differential current from each output current of the first differential amplifier and driving the second differential amplifier based on the differential current. And a frequency multiplier / mixer circuit. 2. The frequency multiplier / mixer circuit according to claim 1, wherein the current mirror circuit is controlled so as to drive the second differential amplifier with a current obtained by subtracting a constant value DC current from the difference current. A frequency multiplying / mixing circuit, comprising: