JP2011072026A - High-frequency amplifier and differential amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency amplifier capable of suppressing its loop oscillation, and a differential amplifier for use in the high-frequency amplifier. <P>SOLUTION: A differential amplifier uses inductors 35, 36 for respective collector or drain loads of transistors 39, 40 constituting a differential couple. In the differential amplifier, resistors 33, 34 are connected in series to the respective inductors 35, 36. Otherwise, one-side terminals of the respective inductors 35, 36 are connected in common and then connected through the resistors to a power terminal 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multistage-connected high-frequency amplifier and a differential amplifier used for the high-frequency amplifier.

  In an amplifier used for an integrated circuit or the like, a differential amplifier is often used for the purpose of reducing the size and reducing the number of pads. Also, as an amplifier load, a resistive load is often used instead of an inductor load for miniaturization. Further, in a circuit block that requires output amplitude, a circuit in which the constant current source on the lower side of the differential amplifier is omitted is often used.

  Conventionally, a high-frequency amplifier having a multi-stage differential amplifier is a three-stage differential amplifier, the second-stage collector is an inductor feed, the first and third-stage collectors are resistance feeds, and the base is all resistance feeds. In the third stage, there is a circuit in which a constant current source is omitted in order to ensure the output amplitude, and the collector voltage is applied in common with three stages (for example, see Non-Patent Document 1).

“Electronic Circuits for Transistors and ICs” (Asakura Shoten, Donald L. Schilling / Charles Belove, translated by Shinnosuke Yamanaka / Koichi Usami), p.308, Figure 8-3-1

  However, in such a conventional high-frequency amplifier, loop oscillation may occur depending on a combination of a collector, a base feed method, and the presence or absence of a constant current source, and it is necessary to separate from a circuit that generates a loop gain.

  Also, in amplifiers with resistors as loads, the low frequency side gain, which was not a problem in one stage, is amplified by multiple stages and becomes higher than the desired wave on the low frequency side, so it oscillates at this frequency. May cause.

  Further, the input / output signal of the amplifier whose symmetry has been lost due to the asymmetry of the layout in the IC chip, etc., may wrap around the base or collector on the opposite side and cause loop oscillation at a high gain frequency.

  The present invention has been made to solve the above problems, and an object thereof is to provide a high-frequency amplifier that suppresses loop oscillation and a differential amplifier used in the high-frequency amplifier.

  The differential amplifier according to the present invention is characterized in that, in a differential amplifier using an inductor as a collector load, a resistor is connected in series with each inductor.

  In addition, after one end of each inductor is made common, it is connected to a power supply terminal through a resistor.

  The high-frequency amplifier according to the present invention is characterized in that the differential amplifier is used as at least one of the amplifiers to form a multistage amplifier.

  According to the present invention, it is possible to eliminate a closed loop circuit having a loop gain of 1 and suppress oscillation.

1 is a circuit diagram showing a high frequency amplifier according to Embodiment 1 of the present invention. FIG. It is a circuit diagram which shows the prior art example used for demonstrating the effect which concerns on the high frequency amplifier by Embodiment 1 of this invention. It is a figure which shows the simulation result of the loop gain shown in FIG. It is a circuit diagram which shows the high frequency amplifier by Embodiment 2 of this invention. It is a circuit diagram which shows the high frequency amplifier which combined Embodiment 1 and 2 of this invention. It is a circuit diagram which shows the differential amplifier by Embodiment 3 of this invention, and its comparative example. It is a figure explaining the further effect of the differential amplifier by Embodiment 3. FIG. It is a circuit diagram which shows the differential amplifier by Embodiment 4 of this invention. It is a circuit diagram which shows the differential amplifier by Embodiment 5 of this invention. It is a circuit diagram which shows the differential amplifier by Embodiment 6 of this invention. It is a circuit diagram which shows the high frequency amplifier by Embodiment 7 of this invention. It is a circuit diagram which shows the differential amplifier by Embodiment 8 of this invention.

Embodiment 1 FIG.
1 is a circuit diagram showing a high-frequency amplifier according to Embodiment 1 of the present invention. The high-frequency amplifier shown in FIG. 1 is a multi-stage differential amplifier, for example, a three-stage differential amplifier. The first-stage differential amplifier has the collector of the transistor 20 serving as a differential pair fed by resistors 12 and 13, respectively. Commonly connected to the voltage terminal 11, the emitter is commonly connected to the constant current source circuit 3 and grounded via the constant current source circuit 3, and the base connected to the positive phase input terminal 1 and the negative phase input terminal 2 is the base voltage terminal They are fed by resistors connected to 5 and 6, respectively.

  In the second-stage differential amplifier, the collectors of the transistors 21 forming a differential pair are commonly connected to the collector voltage terminal 11 via the inductors 14 and 15, respectively, and the emitters are commonly connected to the constant current source circuit 4. Grounded through the circuit 4, the base is fed by a resistor connected to the base voltage terminals 7 and 8, and is connected through the capacitance 23 to the collector of the transistor 20 as a differential pair of the first-stage differential amplifier. ing.

  In the third-stage differential amplifier, the collector of the transistor 22 serving as a differential pair is connected to the positive-phase output terminal 18 and the negative-phase output terminal 19, respectively. The differential pair of the differential amplifier of the second stage is fed by resistors 16 and 17 and commonly connected to the collector voltage terminal 11, and the base is fed by a resistor connected to the base voltage terminals 9 and 10. Is connected to the collector of the transistor 21. The high-frequency ground terminal of the common emitter of the third-stage differential amplifier that ensures the output amplitude is separated and independent from the ground terminals of other amplification stages.

  That is, the high-frequency amplifier shown in FIG. 1 has a three-stage configuration including a third-stage differential amplifier in which the base and collector potentials are fed by resistors and the common emitter of the transistor 22 serving as a differential pair is grounded in terms of high frequency. Only this differential amplifier has a configuration in which the high-frequency ground terminal of the common emitter is independent of the ground terminals of other amplification stages.

  By the way, in the high frequency amplifier shown in FIG. 1, as shown in FIG. 2, the ground terminal of the common emitter of the third stage differential amplifier is connected to the ground terminal of the first and second stage differential amplifiers. In the case of common connection, the simulation results of the loop gains of the loops L12 and L23 shown in FIG. 2 are as shown in FIGS. 3 (a) and 3 (b).

  The loop gain is a ratio of A1 and A1 ′ when A1 is a high-frequency traveling wave from an arbitrary position in the loops L12 and L23 shown in FIG. 2 and A1 ′ is a high-frequency traveling wave returning through the loop path. Can be sought. 3A, G23 is the amplitude characteristic of the gain of the oscillation path of the loop 23, G12 is the amplitude characteristic of the gain of the oscillation path of the loop L12, and in FIG. 3B, P23 is the gain characteristic of the oscillation path of the loop L23. A phase characteristic P12 is a gain phase characteristic of the loop L12 oscillation path 24.

  Conditions for the occurrence of loop oscillation are that | A1 ′ / A1 | ≧ 1 and ∠ (A1 ′ / A1) = 2mπ (m is an integer).

  As shown in the amplitude and phase characteristics G23 and P23 in FIG. 3, the loop gain with the differential amplifier having the collector voltage as the resistance feed, the base voltage as the resistance feed, and no constant current source circuit satisfies the above condition. As a result, loop oscillation may occur. However, since the amplitude and phase characteristics G12 and P12 shown in FIG. 3 do not satisfy this condition, loop oscillation does not occur.

  According to the first embodiment, loop oscillation may occur depending on the combination of the collector, the base feed method, and the presence / absence of the constant current source as described above, and it is necessary to separate from the circuit in which the loop gain occurs.

  In the first embodiment of the present invention, as shown in FIG. 1, the high-frequency ground terminal of the common emitter of the third-stage differential amplifier is separated and independent from the ground terminals of the other amplification stages. 3 can eliminate the closed loop circuit having a loop gain exceeding 1 as indicated by G23 in FIG. 3, and the high frequency amplifier in which the differential amplifiers shown in FIG. 1 are connected in multiple stages can operate stably without oscillation.

Embodiment 2. FIG.
4 is a circuit diagram showing a high frequency amplifier according to Embodiment 2 of the present invention. In the second embodiment shown in FIG. 4, the same parts as those in the first embodiment shown in FIG. In the second embodiment, as shown in FIG. 4, the ground terminal of the common emitter of the transistor 22 which is the differential pair of the third-stage differential amplifier is the differential of the first-stage and second-stage differential amplifiers. The collector voltage terminal 25 connected in common with the ground terminal of the common emitter of the paired transistors 20 and 21 is connected to the collector of the transistor 22 serving as the differential pair of the third-stage differential amplifier. The collector voltage terminal 11 is separated and independent.

  That is, the high-frequency amplifier shown in FIG. 4 feeds the base and collector potentials with resistors 9, 10, 16 and 17, and the third stage difference in which the common emitter of the transistor 22 as a differential pair is grounded in terms of high frequency. This is a multistage high-frequency amplifier including a dynamic amplifier, and only the third-stage differential amplifier has a configuration in which the power supply terminal connected to the collectors of the transistors constituting the differential pair is independent of the power supply terminals of other amplification stages. .

  According to the second embodiment, by separating the collector terminals in this way, the closed loop circuit having a loop gain exceeding G1 shown by G23 in FIG. 3 can be eliminated, and the differential amplifier shown in FIG. The connected high-frequency amplifier can operate stably without oscillation.

  FIG. 5 is a circuit diagram showing a high frequency amplifier obtained by combining the first and second embodiments. In the circuit shown in FIG. 5, the same reference numerals as those in the circuit shown in FIG.

  The circuit shown in FIG. 5 is a multistage high-frequency amplifier including a differential amplifier in which a base and a collector potential are fed by a resistor, and a common emitter of a transistor serving as a differential pair is grounded in terms of high frequency. Only the high frequency ground terminal of the common emitter is independent of the ground terminal of the other amplification stage, and the common power supply terminal connected to the collector of the differential pair is independent of the power supply terminal of the other amplification stage. .

  Thus, by separating the ground terminal and the collector terminal, it is possible to eliminate the closed loop circuit having a loop gain exceeding G1 shown by G23 in FIG. 3, and the high frequency amplifier shown in FIG. 5 operates stably without oscillation. I can do it.

Embodiment 3 FIG.
FIG. 6A is a circuit diagram showing a differential amplifier according to the third embodiment of the present invention, corresponding to the differential amplifier shown in FIG. 6B. In the differential amplifier shown in FIG. 6 (a), the collectors of transistors 39 and 40 forming a differential pair are connected to positive phase output terminals 37 and 38, respectively, and via inductors 35 and 36 and resistors 33 and 34, respectively. The collector is commonly connected to the collector voltage terminal 30 and the capacitance 42, the common emitter is grounded, the base is fed to the resistors 31 and 32, and is connected to the base voltage terminals 28 and 29 via the resistors 31 and 32. Connected to terminals 26 and 27.

  That is, in the differential amplifier shown in FIG. 6A, resistors 33 and 34 are connected in series to the inductors 35 and 36 in the differential amplifier using the inductors 35 and 36 as collector loads.

  According to the third embodiment, as shown in FIG. 6A, when the object of the differential amplifier is broken due to the asymmetry of the layout, the asymmetry of the differential input signal, etc., the loop L is oscillated. However, by loading the resistors 33 and 34 on the collector terminal side which is a loop oscillation path, the loop gain can be sufficiently reduced, so that the loop oscillation can be suppressed.

  Further, it is possible to suppress the loop oscillation due to the loop between the collector terminals when the differential amplifier shown in FIG.

  Next, FIG. 7 is a diagram for explaining further effects of the differential amplifier according to the third embodiment. In FIG. 7, G6b is the gain of the differential amplifier shown in FIG. 6B, and G6a is the gain of the differential amplifier shown in FIG.

  As shown by a gain G6a in FIG. 7, resistors 33 and 34 are loaded on the collector load side of the differential amplifier and grounded by a capacitance (capacitive element) 42, thereby gain at a low frequency other than the desired frequency. Therefore, it is possible to suppress oscillation caused by unnecessary gain at a low frequency.

Embodiment 4 FIG.
FIG. 8 is a circuit diagram showing a differential amplifier according to the fourth embodiment of the present invention. In the fourth embodiment shown in FIG. 8, the same reference numerals as those in the third embodiment shown in FIG. In the fourth embodiment shown in FIG. 8, capacitances 43 and 44 are connected in parallel to resistors 33 and 34 respectively connected in series to the inductors 35 and 36 shown in FIG. 6A.

  According to the fourth embodiment, as shown in FIG. 8, by connecting capacitances 43 and 44 in parallel to resistors 33 and 34 connected in series to the respective inductors 35 and 36, the resistor 33 is used in high frequency. , 34 are short-circuited, and a decrease in gain in the vicinity of a desired wave due to resistance loaded to suppress loop oscillation and low-frequency gain can be suppressed.

  As a result, an effect equivalent to the effect described in the third embodiment can be obtained without sacrificing the high frequency gain.

Embodiment 5 FIG.
FIG. 9 is a circuit diagram showing a differential amplifier according to the fifth embodiment of the present invention. In the differential amplifier shown in FIG. 9, the collectors of transistors 57 and 58 forming a differential pair are connected to positive-phase output terminals 55 and 56, respectively, and are commonly connected to a resistor 52 via inductors 53 and 54. The other end of 52 is connected to a collector voltage terminal 49 and a capacitance 59, a common emitter is grounded, a base is fed to resistors 50 and 51, and is connected to base voltage terminals 47 and 48 via resistors 50 and 51, respectively. Are connected to the positive phase input terminals 45 and 46.

  That is, in the differential amplifier shown in FIG. 9, after one ends of the inductors 53 and 54 are connected in common, they are connected to the collector voltage terminal 49 via the resistor 52.

  According to the fifth embodiment, as shown in FIG. 9, in a differential amplifier using inductors 53 and 54 as a collector load, after one end of each of inductors 53 and 54 is made common, a resistor 52 is used. By connecting to the power supply terminal, the gain at a low frequency other than the desired frequency can be reduced, so that oscillation due to an unnecessary gain at a low frequency can be suppressed.

Embodiment 6 FIG.
FIG. 10 is a circuit diagram showing a differential amplifier according to the sixth embodiment of the present invention. In the sixth embodiment shown in FIG. 10, the same reference numerals as those in the fifth embodiment shown in FIG. In the sixth embodiment shown in FIG. 10, a capacitance 60 is connected to the resistor 52 shown in FIG.

  According to the sixth embodiment, as shown in FIG. 10, in a differential amplifier using inductors 53 and 54 as a collector load, one end of each of inductors 53 and 54 is made common, and then connected resistor 52. By connecting the capacitance 60 in parallel with each other, the resistor 52 is short-circuited at a high frequency, and it is possible to suppress a decrease in gain near the desired wave due to the resistor 52 loaded to suppress loop oscillation and low-frequency gain. I can do it.

  As a result, the same effect as that described in the fifth embodiment can be obtained without sacrificing the high frequency gain.

Embodiment 7 FIG.
FIG. 11 is a circuit diagram showing a high frequency amplifier according to Embodiment 7 of the present invention. In the seventh embodiment shown in FIG. 11, the same reference numerals as those in the sixth embodiment shown in FIG. In the seventh embodiment shown in FIG. 11, a multi-stage high frequency amplifier is configured using at least one of the differential amplifiers shown in the fifth or sixth embodiment. Reference numerals 61 and 62 denote capacitances.

  According to the seventh embodiment, as shown in FIG. 11, in a high frequency amplifier having a configuration in which differential amplifiers using inductors 53 and 54 as collector loads are connected in multiple stages, one end of each of inductors 53 and 54 is shared. After that, by using a differential amplifier in which a resistor 52 connected to a power supply terminal is arranged, or by using a differential amplifier in which a capacitance 60 is connected in parallel to the resistor 52, one end of each stage resistor 52 is made common. When the power supply terminals of each stage are shared, it is possible to suppress loop oscillation between stages that occurs when the target of the differential amplifier breaks down due to factors such as layout asymmetry and differential input signal asymmetry. it can.

  In particular, loop oscillation can be effectively suppressed by using the differential amplifier in the amplification stage that causes the loop gain.

  Further, an effect equivalent to the effect described in the fifth and sixth embodiments can be obtained.

Embodiment 8 FIG.
FIG. 12 is a circuit diagram showing a differential amplifier according to the eighth embodiment of the present invention. The differential amplifier shown in FIG. 12 is a high-frequency amplifier having multi-stage connected amplification stages that use an amplifier having a collector-to-base feedback resistance 72 as at least one amplification stage. Connected to the front side. In FIG. 12, 63 is an input terminal, 64 and 65 are collector voltage terminals, 66 and 67 are base voltage terminals, 68 to 73 are resistors, 75 and 76 are transistors, and 77 is an output terminal.

  According to the eighth embodiment, as shown in FIG. 12, in a multi-stage amplifier using an amplifier having a feedback resistor 72 as at least one amplification stage, the feedback feedback resistor 72 of the amplifier is connected to the front stage side of the interstage coupling capacitor 74. Conventionally, the capacitance of the feedback circuit necessary for applying the collector voltage and the base voltage independently can be omitted. As a result, the amplifier can be reduced in size and cost.

  In the first to eighth embodiments, the high-frequency semiconductor circuit using the bipolar transistor has been described. However, the high-frequency semiconductor circuit using the field effect transistor in which the collector, base, and emitter are replaced with the drain, gate, and source, respectively. The same effect can be obtained in.

  1, 26, 45 Positive phase input terminal, 2, 27, 46 Reverse phase input terminal, 3, 4 Constant current source circuit, 5-10, 28, 29, 47, 48, 66, 67 Base voltage terminal, 11, 25 , 30, 49, 64, 65 Collector voltage terminal, 12, 13, 16, 17, 31 to 34, 50 to 52, 68 to 73 Resistance, 18, 37, 55 Positive phase output terminal, 19, 38, 56 Reverse phase Output terminal, 20-22, 39, 40, 57, 58, 75, 76 transistor, 14, 15, 53, 54 inductor, 23, 24, 42-44, 59, 60-62, 74 capacitance, 63 input terminal, 77 Output terminal.

Claims (5)

In a differential amplifier using an inductor as a collector or drain load,
A differential amplifier characterized in that a resistor is connected in series with each inductor. The differential amplifier according to claim 1.
A differential amplifier characterized in that a capacitance is connected in parallel to a resistor connected in series to each inductor. In a differential amplifier using an inductor as a collector or drain load,
A differential amplifier characterized in that one end of each inductor is made common and then connected to a power supply terminal via a resistor. The differential amplifier according to claim 3.
A differential amplifier characterized in that a capacitance is connected in parallel with a resistor inserted between an inductor, which is a collector or drain load, and a power supply terminal. A high-frequency amplifier characterized in that the differential amplifier according to claim 3 or 4 is used as at least one of the amplifiers to form a multistage amplifier.

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