JP2000286660A - Balanced/unbalanced circuits convertor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized balance/unbalanced circuits convertor which can be constituted of an IC with a small number of inductors and can be applied to high-frequency signals. SOLUTION: The balanced/unbalance circuits convertor is constituted of a bridge circuit composed of two inductors 101 and 102 and two capacitors 103 and 104, and the values of the inductors 101, 102 and capacitors 103, 104 are set so that the circuit may resonate at a frequency higher than that of a desired signal to be subjected to balanced/unbalanced circuits conversion. A mechanism 109 which can attenuate the resonance frequency of the bridge circuit and can maintain the magnitude of the desired signal is installed to the unbalanced conversion output terminal 107 of the bridge circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a circuit (balun circuit) for converting a balanced (differential) signal into an unbalanced signal,
In particular, it relates to a circuit that can be formed on an integrated circuit.

[0002]

2. Description of the Related Art Differential circuits as shown in FIG. 11 are used in analog circuits because of their good distortion characteristics and little influence on fluctuations in power supply voltage. In the figure, 1101 is a differential circuit, 1102 is a balanced / unbalanced conversion circuit, 1103 is a pad, 1104 is a bonding wire, and 1105 is an interface pin. When such a differential circuit is configured as an integrated circuit, since the number of interface pins 1105 of the envelope is limited, it is possible to convert a balanced (differential) signal line into an unbalanced signal line inside the integrated circuit. Desired.

As such a balanced / unbalanced conversion circuit, for example, there is a circuit using a transformer 1201 as shown in FIG. However, it is difficult to configure a transformer on an IC.

FIG. 13 shows a configuration of a balanced / unbalanced conversion circuit that can be implemented as an IC. In the figure, 1301 is an operational amplifier, and 1302 to 1305 are resistors. However, in order to operate as a balanced / unbalanced conversion circuit, it is required that the gain and differential input of the operational amplifier 1301 are extremely large values (ideally, infinite). The frequency at which the characteristics can be maintained is up to about several MHz at most, and cannot be used for signals of higher frequencies.

A balanced / unbalanced conversion circuit which can be constructed on an IC and is applicable to high frequency signals is disclosed in
-116368 has been proposed. However, in this configuration, since three spiral inductor elements requiring an extremely large area are used as elements on the IC, there is a problem that the chip size is increased and the cost is increased.

[0006]

As described above, it is difficult to configure a transformer on a IC as a component of the balanced / unbalanced conversion circuit, and the operational frequency of the operational amplifier is about several MHz at most. No further high frequency signals can be handled.

[0007] Further, since the spiral inductor requires a large area for its construction and increases the cost, it is necessary to reduce the number of spiral inductors used as much as possible.

An object of the present invention is to realize a small-sized balanced / unbalanced circuit which can be formed on an IC with a smaller number of inductors and can be applied to a high-frequency signal as compared with the methods proposed so far.

[0009]

To achieve the above object, a balanced / unbalanced conversion circuit according to the present invention comprises a bridge circuit of two inductors and two capacitors, and a desired signal for performing balanced / unbalanced conversion. The values of the inductor and the capacitor are set so as to resonate at a frequency higher than the frequency of the output signal, and a mechanism capable of attenuating the resonance frequency of the bridge circuit and maintaining the magnitude of the desired signal is provided at the unbalanced conversion output terminal. .

According to the present invention, a high-frequency signal balance / unbalance conversion circuit, which has conventionally been constituted by independent components, can be formed on an integrated circuit, and the number of interface pins of an envelope of the integrated circuit is reduced. As a result, the size and cost can be reduced, and the peripheral components used as the balance / unbalance conversion circuit can be reduced, so that the size and cost of the device can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configuration and operation of a balanced / unbalanced conversion circuit according to the present invention will be described with reference to FIG.

A bridge circuit is formed by the inductors 101 and 102 and the capacitors 103 and 104. The values of the inductors 101 and 102 are L1 and L2, respectively. Similarly, the values of the capacitors 103 and 104 are respectively set to C
1, C2. Inductor 101 and capacitor 103
Is grounded in an AC manner, and a connection point 105 between the inductor 101 and the capacitor 104 and an inductor 102
A connection point 106 between the capacitor and the capacitor 103 is a differential input.
As shown in FIG. 1, when an AC voltage V ₁ having a frequency f is applied to the connection point 105 and an AC voltage V ₂ having a frequency f is applied to the connection point 106, the current i flowing through the bridge circuit and the voltage V _{1 and the} voltage V ₂
Can be expressed by the following equation.

[0013]

(Equation 1)

At this time, the connection point 107 between the inductor 102 and the capacitor 104 is set as an unbalanced output, and the output voltage V
_{If 3} occurs,

[0015]

(Equation 2)

Therefore, from the equations (1) and (2), the input / output characteristics of the balanced / unbalanced conversion circuit shown in FIG. 1 are expressed by the following equations.

[0017]

(Equation 3)

Therefore, when ω ² C2L2 = 1 and C1 ≠ C2 from equation (4), the right side of equation (4) becomes infinite, and the bridge circuit resonates. However, 1-ω ² C2L
If 2 ≠ 1, the right side of equation (4) is a constant value determined by the relationship between C1 and C2.

For example, C2 = 1 pF, L2 = 1.583
Assuming 1 nH, for a signal of frequency f = 2 GHz, ω ²
C2L2 = 1/4. If C2 = C1 = 1 pF, the numerator of equation (4) becomes the same as the denominator, that is, V ₃ /
(V ₁ −V ₂ ) = 1. Generally, the value of the inductor that can be configured on the integrated circuit is up to about ten and several nH, but the inductor and the capacitor having the values of C1 and L2 set in this example are the values that can be configured on the integrated circuit.

However, in the configuration of this embodiment, ω ′ ² C2L2 = 1 (where ω ′ = 2π) for a signal of f ′ = 4 GHz.
f '). Further, since it is practically difficult to make the capacitors 103 and 104 have exactly the same value, C2
≠ C1, and therefore the bridge circuit may resonate. To solve this problem, a circuit 109 having the characteristic of attenuating the resonance frequency f 'and maintaining the signal level of the desired frequency f may be provided at the unbalanced output terminal 107 as shown in FIG.

Here, if the frequency f, the inductor 102, and the capacitor 104 are set so that ω ² C2L2 <1, the resonance frequency f ′ of the bridge circuit in FIG. 1 becomes f ′> f. Therefore, the mechanism 10 for cutting off the resonance frequency f '
Reference numeral 9 denotes a resonance frequency attenuating circuit 409 having a low-pass / high-frequency cutoff characteristic as shown in FIG. For example, the cut-off frequency fc determined by the impedance of the post-stage circuit connected to the resistor 410 and the unbalanced output 407 and the value of the capacitor 411 is set so that f <fc <f ′.
And the value of the capacitor 411 may be set.

Conversely, if the frequency f, the impedance 102, and the capacitor 104 are set so that ω ² C1L2> 1, the resonance frequency f ′ becomes f ′ <f, and the mechanism 109 provides high-pass / low-pass cutoff characteristics. What should be done is inductor 1
02, it is necessary to increase the value of the capacitor 104,
In particular, regarding the capacitor 104, the capacitance value and the area required on the integrated circuit are in a proportional relationship, and it is more advantageous to set ω ² C1L2 <1 from the viewpoint of reducing the area of the integrated circuit.
However, depending on the desired frequency f, the inductor 101,
102 and the values of the capacitors 103 and 104 become smaller,
When fabricated on an integrated circuit, accuracy may be poor or fabrication may not be possible. To avoid such a problem, ω ² C1L2> 1 may be set.

The resonance frequency attenuating circuit may be provided at the balanced input terminals 205 and 206 (305 and 306 in FIG. 3) as shown in FIG. 2 or FIG.

FIG. 5 is a graph showing an example of the input / output characteristics of the circuit shown in FIG. The circuit having the characteristics shown in FIG. 5 sets the desired frequency f to 2 GHz and the resonance frequency f 'to 4 GHz.
It was set to become. In the desired signal, the level of the balanced input voltage and the level of the unbalanced output voltage are almost equal, and the signal at the resonance frequency is attenuated to a level that does not cause any problem, indicating that the signal functions as a balanced-unbalanced conversion circuit. .

Incidentally, the balanced / unbalanced conversion circuit shown in FIG. 1 transmits a signal by voltage, and the subsequent stage of the balanced / unbalanced conversion circuit needs to be set to the highest possible impedance. For example, it can be realized by a common collector circuit 510 as shown in FIG. 6 or a common source circuit 610 as shown in FIG. Although an FET is used for the common source circuit 610, a MOSFET can of course be used. Further, according to the configuration shown in FIG. 8, the inductor 702 constituting the balanced / unbalanced conversion circuit can also serve as a bias circuit for supplying a base current of the emitter follower circuit 711 in the subsequent stage, and the elements constituting the circuit The number can be reduced.

Alternatively, as shown in FIG. 9, it is possible to reduce the number of elements by configuring the elements constituting the balanced / unbalanced conversion circuit, the load of the differential amplifier, and the bias element. In this case, since the capacitor 804 cannot pass a DC bias, the resistor 816 is connected in parallel. The values of the inductors 801 and 802 are respectively L1 and L
2. When the values of the capacitors 803 and 804 are C1 and C2 and the value of the resistor 816 is R, the input / output characteristics of the balanced / unbalanced conversion circuit are as follows.

[0027]

(Equation 4)

Therefore, if R >> 1 / ωC2,
Equation (5) can be regarded as substantially the same as equation (3).
However, if the value R of the resistor 816 is increased, a difference occurs in the collector voltages of the transistors 809 and 810 forming the differential pair due to the voltage drop effect of the resistor 816, and the operation of the differential pair becomes unbalanced, and the characteristics may be deteriorated. There is. In order to avoid this problem, a balanced / unbalanced conversion circuit may be configured as shown in FIG. In the case of the configuration of FIG. 10, the values of the inductors 901, 902, and 903 are L1, L
2, L3 and the value of the capacitor 904 is C1,
The input / output characteristics of the balanced / unbalanced conversion circuit

[0029]

(Equation 5)

For example, C1 = 1 pF, L2 = 1.483n
Ω ² for a signal of frequency f = 2 GHz when H
C1L2 = 1/4. Therefore, the denominator of equation (7) is 3/4. At this time, the value of the inductor L3 is L3 =
Assuming 3.166 nH, the numerator of equation (7) is 3/4, and the voltage gain of the balanced-unbalanced conversion circuit is 1. Referring to the bridge circuit having the configuration shown in FIG. 10, the topology of this circuit is the same as that of the balun circuit disclosed in Japanese Patent Application Laid-Open No. Hei 9-116368. There is novelty in that it also serves as a bias circuit for the differential circuit in the preceding stage, and can be configured with smaller elements.

[0031]

As described above, according to the present invention, a high-frequency signal balanced / unbalanced conversion circuit can be realized on an integrated circuit, and the size and cost of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a configuration example different from the first embodiment of the present invention.

FIG. 3 is a view for explaining an example of a different configuration of the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a resonance frequency attenuation circuit used in the first embodiment of the present invention.

FIG. 5 is a diagram showing an example of characteristics of the circuit of the present invention.

FIG. 6 is a diagram for explaining a second embodiment of the present invention.

FIG. 7 is a diagram for explaining a configuration example different from the second embodiment of the present invention.

FIG. 8 is a diagram for explaining a third embodiment of the present invention.

FIG. 9 is a diagram for explaining a fourth embodiment of the present invention.

FIG. 10 is a diagram for explaining a different configuration example of the fourth embodiment of the present invention.

FIG. 11 is a diagram illustrating an effect when the present invention is applied to an integrated circuit.

FIG. 12 is a view for explaining a conventional example.

FIG. 13 is a view for explaining a conventional example.

[Explanation of symbols]

101, 102: Inductor, 103, 104: Capacitor 105, 106: Balanced (differential) input terminal, 107: Unbalanced output terminal 108: Ground terminal, 109: Resonance frequency signal attenuating circuit 201, 202: Inductor, 203, 204 ... Capacitors 205, 206 ... Balanced (differential) input terminal, 207 ... Unbalanced output terminal 208 ... Ground terminal, 209 ... Resonance frequency signal attenuating circuit 301,302 ... Inductor, 303,304 ... Capacitor 305,306 ... Balanced (difference) Operation) input terminal, 307 unbalanced output terminal 308 ground terminal, 309, 310 resonance frequency signal attenuating circuit 401, 402 inductor, 403, 404, 411
... Capacitors 405, 406 balanced (differential) input end, 407 unbalanced output end 408 grounded end, 409 resonance frequency signal attenuating circuit, 4
DESCRIPTION OF SYMBOLS 10 ... Resistor 501, 502 ... Inductor 503, 504, 508, 509 ... Capacitor 505, 506 ... Balanced (differential) input terminal 507 ... Unbalanced output terminal, 508 ... Ground terminal, 510 ... Emitter follower circuit 511 ... Emitter follower circuit Output end, 601, 602
... Inductors 603, 604, 608, 609 ... Capacitors 605, 606 ... Balanced (differential) input terminal, 607 ... Unbalanced output terminal 608 ... Ground terminal, 610 ... Emitter follower circuit 611 ... Emitter follower circuit output terminal, 701, 702
... Inductors 703, 704, 708 ... Capacitors 705, 706 ... Balanced (differential) input terminal, 707 ... Unbalanced output terminal 708 ... Ground terminal, 709 ... Resistance, 710 ... Emitter follower circuit 711 ... Base bias current, 801, 802 ... Inductors 803, 804, 814, 815 ... Capacitors 805, 806 ... Balanced (differential) input end, 807 ... Unbalanced output end 808 ... AC ground end, 809, 810 ... Differential pair transistors 811, 812, 816 ... Resistance , 813 ... constant current sources 901, 902, 903 ... inductors 904, 914, 915 ... capacitors 905, 906 ... balanced (differential) input terminals, 907 ... unbalanced output terminals 908 ... AC ground terminals, 909, 910 ... differential Paired transistors 911, 912 ... resistance, 913 ... constant current source, 1001 ...
Desired signal frequency 1002 Bridge circuit resonance frequency 1101 Differential circuit 1102 Balance-unbalance conversion circuit 1103 Pad 1104 Bonding wire 1105 Interface pin 1201 Transformer 1301 Operational amplifier 1302, 1303, 1304, 1305 …resistance

Claims (7)

[Claims] 1. A balanced / unbalanced conversion circuit comprising a bridge circuit having at least two inductors and capacitors, wherein one of four connection terminals of the bridge circuit is AC grounded, and A balanced / unbalanced conversion circuit, wherein two of the connection terminals are configured as balanced signal input terminals, and the connection terminal different from the balanced signal input terminal is configured as an unbalanced signal output terminal. 2. The first and second inductors and the first and second inductors.
A balanced-unbalanced conversion circuit including a bridge circuit having a capacitor, wherein one end of the first inductor and one end of the first capacitor are AC grounded, and the other end of the first inductor and the second One end of the capacitor is connected together and configured as a first balanced signal input end; the other end of the first capacitor and one end of the second inductor are connected together and configured as a second balanced signal input end; The other end of the capacitor and the other end of the second inductor are connected together, and are configured as an unbalanced signal output end. 3. The value of the inductor and the capacitor constituting the balanced-unbalanced conversion circuit is set so that the resonance frequency of the bridge circuit is different from the desired signal frequency for performing the balanced-unbalanced conversion. Claim 1.
Or the balanced-unbalanced conversion circuit according to 2. 4. An attenuating circuit is provided at the unbalanced signal output terminal and / or the balanced signal input terminal, wherein the attenuating circuit has a characteristic of attenuating a frequency signal corresponding to a resonance frequency of the bridge circuit. The balanced / unbalanced conversion circuit according to any one of claims 1 to 3, wherein: 5. The balanced / unbalanced conversion circuit according to claim 1, wherein the inductor and the capacitor constituting the bridge circuit are all configured on an integrated circuit. 6. The balanced-unbalanced conversion circuit according to claim 1, wherein an element constituting the bridge circuit also operates as a bias element of a circuit connected to a stage subsequent to the bridge circuit. 7. The balanced / unbalanced conversion circuit according to claim 1, wherein the elements constituting the bridge circuit also operate as a load element and a bias supply element of a differential circuit.