US20020021174A1 - Variable gain amplifier with high linearity and low noise - Google Patents
Variable gain amplifier with high linearity and low noise Download PDFInfo
- Publication number
- US20020021174A1 US20020021174A1 US09/163,892 US16389298A US2002021174A1 US 20020021174 A1 US20020021174 A1 US 20020021174A1 US 16389298 A US16389298 A US 16389298A US 2002021174 A1 US2002021174 A1 US 2002021174A1
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- differential amplifier
- amplifier stage
- current
- signal
- differential
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/4508—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using bipolar transistors as the active amplifying circuit
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G1/00—Details of arrangements for controlling amplification
- H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
- H03G1/0017—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal the device being at least one of the amplifying solid-state elements
- H03G1/0023—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal the device being at least one of the amplifying solid-state elements in emitter-coupled or cascode amplifiers
Definitions
- This invention relates to electronic circuits, and more particularly to an electronic variable gain amplifier with high linearity and low noise.
- the received signal has a high dynamic range (>80 dB).
- a variable gain amplifier (VGA) with equivalent or better dynamic range is required. It is desirable that the VGA exhibit low noise when a small signal is present at the input in a high gain mode, and yet be able to handle a large input signal when in a low gain mode. Accordingly, the VGA should exhibit high linearity in low gain mode.
- Known solutions fail to provide a VGA that has sufficiently low noise, high linearity, linear gain control, temperature stable gain control, and a high dynamic range that are all suitable for some applications (such as a code division multiple access (CDMA) receiver).
- CDMA code division multiple access
- the present invention provides such an amplifier.
- the invention includes a variable gain amplifier that has a high linearity gain stage coupled with a low noise gain stage, and a steering circuit that steers the input signal between these two stages.
- the preferred embodiment employs steering of the input signal and extensive linearization (in dB) of the control signal to provide stable and linear gain control and high dynamic range.
- the invention includes a first differential amplifier stage having low noise (i.e., no emitter degeneration in a bipolar implementation) and configured to receive a differential input signal and contribute to an output signal current; a second differential amplifier stage that has higher linearity than the first differential amplifier stage (but has more noise, i.e., exhibits emitter degeneration in a bipolar implementation), and configured to receive the differential input signal and contribute to the output signal current; a first current source coupled to the first differential amplifier stage and regulated by a control signal x according to the formula I*(k ⁇ x), where k is a constant and x is a variable ranging from 0 to k; a second current source coupled to the second differential amplifier stage and regulated by a control signal x according to the formula I*(x); and a signal steering circuit, coupled to the first and second differential amplifier stages, for steering the output signal current from the first and second differential amplifier stages either to a voltage source or to a corresponding load.
- a first current source coupled to the first differential amplifier stage and regulated
- FIG. 1 is a schematic diagram of the preferred embodiment of the present invention.
- FIG. 1 shows a schematic diagram of a preferred embodiment of the present invention.
- the inventive circuit is shown as being implemented in bipolar circuitry.
- CMOS complimentary metal oxide semiconductor
- FET field effect transistors
- differential IF inputs IN+, IN ⁇ are respectively coupled to the bases of transistors Q 1 , Q 3 , and Q 2 , Q 4 .
- Transistors Q 1 and Q 2 along with current source I 2 , form a first differential amplifier stage with low noise (no emitter degeneration in the illustrated bipolar embodiment).
- Transistors Q 3 and Q 4 along with resistors R 1 and R 2 and current source I 1 , form a second differential amplifier stage with higher linearity than the Q 1 , Q 2 amplifier stage but also higher noise (emitter degenerated in the illustrated bipolar embodiment).
- the input signal current passes through load resistors R 3 and R 4 to obtain a voltage gain at output terminals OUT+, OUT ⁇ .
- the current sources I 1 , I 2 are regulated by a control signal x, which is varied between values of “0” and “k”, where k is a constant. In the preferred embodiment, k equals 2.
- a control signal x is varied between its minimum and maximum values, current will be shared between the two differential amplifier stages in accordance with the formulas shown in FIG. 1. At each limit of the control range, one amplifier stage will be fully on, while the other amplifier stage will be starved of current and thus fully off.
- the control signal x is set under user control, in known fashion.
- transistors Q 5 , Q 6 , Q 7 , and Q 8 act to steer the signal current from the input differential pairs Q 1 , Q 2 and Q 3 , Q 4 , respectively, either to a voltage source ⁇ overscore (V) ⁇ cc (through transistors Q 6 and Q 7 ), or to the load resistors R 3 , R 4 (through transistors Q 5 and Q 8 ).
- the steering signal for transistors Q 5 , Q 6 , Q 7 , and Q 8 is the output of a voltage source V1 that is preferably related to the control signal x in such a way as to produce an overall linear gain versus control signal response.
- transistors Q 5 and Q 8 are steered by a voltage that is proportional to a current I*x from current source I 5
- transistors Q 6 and Q 7 are steered by a voltage that is proportional to a current I*(k ⁇ x) from current source I 6 , where x and k are as defined above.
- Current sources I 3 and I 4 act to maintain some standing currents through transistors Q 1 , Q 2 and Q 3 , Q 4 , respectively, so that as one of the amplifier stages starts to turn on, none of its signal current will reach the load resistors R 3 , R 4 until the emitter current for the transistors in that stage equals the associated hold off current for such transistors. For example, no signal current from transistors Q 1 and Q 2 reaches the load resistors R 3 , R 4 until current source I 2 has a value greater than I holdoff . This feature enables the circuit to maintain its linearity across a wider control signal range, controllable by the value of I holdoff compared to the value of current sources I 1 and I 2 .
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Amplification And Gain Control (AREA)
Abstract
A variable gain amplifier that has a high linearity gain stage coupled with a low noise gain stage, and a steering circuit that steers the input signal between these two stages depending on the gain requirement. The preferred embodiment employs steering of the input signal and extensive linearization (in dB) of the control signal to provide stable and linear gain control and high dynamic range. One embodiment includes a first differential amplifier stage having no emitter degeneration and configured to receive a differential input signal and contribute to an output signal current; a second differential amplifier stage having emitter degeneration and higher linearity than the first differential amplifier stage, and configured to receive the differential input signal and contribute to the output signal current; a first current source coupled to the first differential amplifier stage and regulated by a control signal X according to the formula I*(K−x), where K is a constant and x is a variable ranging from 0 to K; a second current source coupled to the second differential amplifier stage and regulated by a control signal X according to the formula I*(x); and a signal steering circuit, coupled to the first and second differential amplifier stages, for steering the output signal current from the first and second differential amplifier stages either to a voltage source or to a corresponding load resistor.
Description
- This application is related to co-pending U.S. Patent Application No. ______ , entitled “VARIABLE GAIN AMPLIFIER WITH GAIN LINEAR WITH CONTROL VOLTAGE”, filed ______ , and assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference.
- This invention relates to electronic circuits, and more particularly to an electronic variable gain amplifier with high linearity and low noise.
- In a radio frequency (RF) transceiver, the received signal has a high dynamic range (>80 dB). In order to supply a signal of constant amplitude to a baseband section of the transceiver, a variable gain amplifier (VGA) with equivalent or better dynamic range is required. It is desirable that the VGA exhibit low noise when a small signal is present at the input in a high gain mode, and yet be able to handle a large input signal when in a low gain mode. Accordingly, the VGA should exhibit high linearity in low gain mode. Known solutions fail to provide a VGA that has sufficiently low noise, high linearity, linear gain control, temperature stable gain control, and a high dynamic range that are all suitable for some applications (such as a code division multiple access (CDMA) receiver).
- Accordingly, the inventor has perceived that there is a need for a variable gain amplifier which has such characteristics. The present invention provides such an amplifier.
- The invention includes a variable gain amplifier that has a high linearity gain stage coupled with a low noise gain stage, and a steering circuit that steers the input signal between these two stages. The preferred embodiment employs steering of the input signal and extensive linearization (in dB) of the control signal to provide stable and linear gain control and high dynamic range.
- In particular, in one aspect the invention includes a first differential amplifier stage having low noise (i.e., no emitter degeneration in a bipolar implementation) and configured to receive a differential input signal and contribute to an output signal current; a second differential amplifier stage that has higher linearity than the first differential amplifier stage (but has more noise, i.e., exhibits emitter degeneration in a bipolar implementation), and configured to receive the differential input signal and contribute to the output signal current; a first current source coupled to the first differential amplifier stage and regulated by a control signal x according to the formula I*(k−x), where k is a constant and x is a variable ranging from 0 to k; a second current source coupled to the second differential amplifier stage and regulated by a control signal x according to the formula I*(x); and a signal steering circuit, coupled to the first and second differential amplifier stages, for steering the output signal current from the first and second differential amplifier stages either to a voltage source or to a corresponding load.
- The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
- FIG. 1 is a schematic diagram of the preferred embodiment of the present invention.
- Like reference numbers and designations in the various drawings indicate like elements.
- FIG. 1 shows a schematic diagram of a preferred embodiment of the present invention. The inventive circuit is shown as being implemented in bipolar circuitry. However, a comparable circuit can be implemented in other technologies, such as complimentary metal oxide semiconductor (CMOS) field effect transistors (FET). Accordingly, the embodiment shown in FIG. 1 should be taken as exemplary only.
- In the preferred embodiment, differential IF inputs IN+, IN−are respectively coupled to the bases of transistors Q 1, Q3, and Q2, Q4. Transistors Q1 and Q2, along with current source I2, form a first differential amplifier stage with low noise (no emitter degeneration in the illustrated bipolar embodiment). Transistors Q3 and Q4, along with resistors R1 and R2 and current source I1, form a second differential amplifier stage with higher linearity than the Q1, Q2 amplifier stage but also higher noise (emitter degenerated in the illustrated bipolar embodiment). The input signal current passes through load resistors R3 and R4 to obtain a voltage gain at output terminals OUT+, OUT−.
- The current sources I 1, I2 are regulated by a control signal x, which is varied between values of “0” and “k”, where k is a constant. In the preferred embodiment, k equals 2. As the control signal x is varied between its minimum and maximum values, current will be shared between the two differential amplifier stages in accordance with the formulas shown in FIG. 1. At each limit of the control range, one amplifier stage will be fully on, while the other amplifier stage will be starved of current and thus fully off. The control signal x is set under user control, in known fashion.
- To further improve the dynamic range of the variable gain amplifier section, transistors Q 5, Q6, Q7, and Q8 act to steer the signal current from the input differential pairs Q1, Q2 and Q3, Q4, respectively, either to a voltage source {overscore (V)}cc(through transistors Q6 and Q7), or to the load resistors R3, R4 (through transistors Q5 and Q8). The steering signal for transistors Q5, Q6, Q7, and Q8 is the output of a voltage source V1 that is preferably related to the control signal x in such a way as to produce an overall linear gain versus control signal response. In particular, transistors Q5 and Q8 are steered by a voltage that is proportional to a current I*x from current source I5, and transistors Q6 and Q7 are steered by a voltage that is proportional to a current I*(k−x) from current source I6, where x and k are as defined above. Further details of a suitable voltage source for generating the desired control signal output are taught in the above-referenced co-pending U.S. patent application.
- In an alternative embodiment, V1 may equal a bias voltage, V bias, plus Vref*(x−k/2), where x and k are as defined above, and Vref is a reference voltage. If k=2, V1 equals Vbias+Vref*(X−1). As the control signal x is varied between its minimum and maximum values (0 to k, in this example), V1 ranges from Vbias−Vref to Vbias+Vref.
- Current sources I 3 and I4 act to maintain some standing currents through transistors Q1, Q2 and Q3, Q4, respectively, so that as one of the amplifier stages starts to turn on, none of its signal current will reach the load resistors R3, R4 until the emitter current for the transistors in that stage equals the associated hold off current for such transistors. For example, no signal current from transistors Q1 and Q2 reaches the load resistors R3, R4 until current source I2 has a value greater than Iholdoff. This feature enables the circuit to maintain its linearity across a wider control signal range, controllable by the value of Iholdoff compared to the value of current sources I1 and I2.
- A number of embodiments of the present invention have been described. Neverthe-less, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
Claims (10)
1. A variable gain amplifier including:
(a) a first differential amplifier stage having low noise and configured to receive a differential input signal and contribute to an output signal current;
(b) a second differential amplifier stage having higher linearity than the first differential amplifier stage, and configured to receive the differential input signal and contribute to the output signal current;
(c) a first current source coupled to the first differential amplifier stage and regulated by a control signal x according to the formula I*(k−x), where k is a constant and x is a variable ranging from 0 to k;
(d) a second current source coupled to the second differential amplifier stage and regulated by the control signal x according to the formula I*(x); and
(e) a signal steering circuit, coupled to the first differential amplifier stage and the second differential amplifier stage, for steering the output signal current from the first differential amplifier stage and the second differential amplifier stage either to a voltage source or to a corresponding load.
2. The variable gain amplifier of claim 1 , further including a first standing current source coupled to the first differential amplifier stage and a second standing current source coupled to the second differential amplifier stage, for maintaining a standing current to each such differential amplifier stage for improved linearity.
3. The variable gain amplifier of claim 1 , wherein k equals two.
4. The variable gain amplifier of claim 1 , further including a voltage source coupled to the signal steering circuit for providing a control voltage V1 that is related to the control signal x so as to produce an overall linear gain versus control signal response.
5. The variable gain amplifier of claim 4 , wherein V1 equals a bias voltage, Vbias, plus Vref*(X−k/2), where Vref is a reference voltage.
6. A method of varying gain in an amplifier circuit, including the steps of:
(a) applying a differential input signal to a first differential amplifier stage having low noise and configured to contribute to an output signal current;
(b) applying the differential input signal to a second differential amplifier stage having higher linearity than the first differential amplifier stage, and configured to contribute to the output signal current;
(c) varying current to the first differential amplifier stage in response to a control signal x according to the formula I*(k−x), where k is a constant and x is a variable ranging from 0 to k;
(d) varying current to the second differential amplifier stage in response to the control signal x according to the formula I*(x); and
(e) steering the output signal current from the first differential amplifier stage and the second differential amplifier stage either to a voltage source or to a corresponding load resistor.
7. The method of 6, further including the step of maintaining a standing current to each of the first and second differential amplifier stages for improved linearity.
8. The method of 6, wherein k equals two.
9. The method of 6, wherein the step of steering the output signal current includes applying a control voltage V1 that is related to the control signal x so as to produce an overall linear gain versus control signal response.
10. The method of 9, wherein V1 equals a bias voltage, Vbias, plus Vref*(x−k2), where Vref is a reference voltage.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/163,892 US6445251B1 (en) | 1998-09-30 | 1998-09-30 | Variable gain amplifier with high linearity and low noise |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/163,892 US6445251B1 (en) | 1998-09-30 | 1998-09-30 | Variable gain amplifier with high linearity and low noise |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| US20020021174A1 true US20020021174A1 (en) | 2002-02-21 |
| US6445251B1 US6445251B1 (en) | 2002-09-03 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US09/163,892 Expired - Lifetime US6445251B1 (en) | 1998-09-30 | 1998-09-30 | Variable gain amplifier with high linearity and low noise |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US6445251B1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8742846B1 (en) | 2013-03-14 | 2014-06-03 | Hittite Microwave Corporation | Selectable gain differential amplifier |
| WO2020125953A1 (en) * | 2018-12-18 | 2020-06-25 | Huawei Technologies Co., Ltd. | Linear wide-range variable gain amplifier for broadband applications |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6684065B2 (en) * | 1999-12-20 | 2004-01-27 | Broadcom Corporation | Variable gain amplifier for low voltage applications |
| US6711391B1 (en) | 2000-10-10 | 2004-03-23 | Qualcomm, Incorporated | Gain linearizer for variable gain amplifiers |
| US6798290B2 (en) * | 2001-08-31 | 2004-09-28 | Sequoia Communications | Translinear variable gain amplifier |
| US6566951B1 (en) * | 2001-10-25 | 2003-05-20 | Lsi Logic Corporation | Low voltage variable gain amplifier having constant common mode DC output |
| DE10312436A1 (en) * | 2003-03-20 | 2004-10-07 | Infineon Technologies Ag | Voltage-controlled oscillator circuit for transmission and reception system in communications device with variable capacitance storage capacitor for adjustment of oscillator frequency |
| KR100736394B1 (en) * | 2005-11-01 | 2007-07-09 | 삼성전자주식회사 | Differential Circuit with Improved Linearity, Differential Amplifier and Mixer Circuit |
| JP4837395B2 (en) * | 2006-02-22 | 2011-12-14 | ルネサスエレクトロニクス株式会社 | Operational amplifier |
| US7486135B2 (en) * | 2007-05-29 | 2009-02-03 | Telefonaktiebolaget Lm Ericsson (Publ) | Configurable, variable gain LNA for multi-band RF receiver |
| US7701289B2 (en) * | 2007-10-24 | 2010-04-20 | Industrial Technology Research Institute | Variable gain amplifier including series-coupled cascode amplifiers |
| US8351887B2 (en) * | 2009-12-07 | 2013-01-08 | CSR Technology, Inc. | Systems and methods providing multi-path low noise amplifiers with seamless switching |
| US11595008B2 (en) | 2020-01-09 | 2023-02-28 | Skyworks Solutions, Inc. | Low noise amplifiers with low noise figure |
| US11817829B2 (en) | 2021-01-29 | 2023-11-14 | Skyworks Solutions, Inc. | Multi-mode broadband low noise amplifier |
| US12212294B2 (en) | 2021-09-24 | 2025-01-28 | Skyworks Solutions, Inc. | Low noise amplifiers with gain steps provided by bypass stage and current steering |
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| US4227256A (en) * | 1978-01-06 | 1980-10-07 | Quadracast Systems, Inc. | AM Broadcast tuner with automatic gain control |
| US4464633A (en) * | 1982-03-31 | 1984-08-07 | Rca Corporation | Amplifier incorporating gain distribution control for cascaded amplifying stages |
| US4818951A (en) * | 1988-04-11 | 1989-04-04 | Peavey Electronics Corporation | Gain control or multiplier circuits |
| JP2986832B2 (en) | 1990-03-13 | 1999-12-06 | 三菱電機株式会社 | Variable gain amplifier |
| US5047731A (en) | 1990-09-05 | 1991-09-10 | Hewlett-Packard Company | Variable gain wideband bipolar monolithic amplifier |
| DE69323483T2 (en) * | 1993-04-06 | 1999-06-24 | Stmicroelectronics S.R.L., Agrate Brianza, Mailand/Milano | Variable gain control for arrangements with low supply voltage |
| EP0632583B1 (en) | 1993-06-30 | 1997-09-03 | STMicroelectronics S.r.l. | Variable gain amplifier |
| US5451901A (en) | 1994-07-01 | 1995-09-19 | Cirrus Logic Inc. | Transconductance amplifiers and exponential variable gain amplifiers using the same |
| US5467057A (en) | 1994-10-11 | 1995-11-14 | Motorola, Inc. | Circuit and method of varying amplifier gain |
| JPH08130428A (en) | 1994-10-28 | 1996-05-21 | Sony Corp | Variable gain amplifier |
| US5977828A (en) * | 1997-12-12 | 1999-11-02 | Nortel Networks Corporation | Multiple-tail transconductance switchable gain amplifer |
-
1998
- 1998-09-30 US US09/163,892 patent/US6445251B1/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8742846B1 (en) | 2013-03-14 | 2014-06-03 | Hittite Microwave Corporation | Selectable gain differential amplifier |
| WO2020125953A1 (en) * | 2018-12-18 | 2020-06-25 | Huawei Technologies Co., Ltd. | Linear wide-range variable gain amplifier for broadband applications |
| CN113196655A (en) * | 2018-12-18 | 2021-07-30 | 华为技术有限公司 | Linear wide range variable gain amplifier for wideband applications |
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| Publication number | Publication date |
|---|---|
| US6445251B1 (en) | 2002-09-03 |
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