GB2211044A - Linear differential amplifier - Google Patents
Linear differential amplifier Download PDFInfo
- Publication number
- GB2211044A GB2211044A GB8723674A GB8723674A GB2211044A GB 2211044 A GB2211044 A GB 2211044A GB 8723674 A GB8723674 A GB 8723674A GB 8723674 A GB8723674 A GB 8723674A GB 2211044 A GB2211044 A GB 2211044A
- Authority
- GB
- United Kingdom
- Prior art keywords
- transistor
- emitter
- differential amplifier
- collector
- base
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- 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
- H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
- H03F3/45197—Pl types
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3211—Modifications of amplifiers to reduce non-linear distortion in differential amplifiers
-
- 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
- H03F3/45098—PI types
- H03F3/45103—Non-folded cascode stages
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Amplifiers (AREA)
Abstract
The amplifier has a small signal gain characteristic which is linear and independent of device temperature. The amplifier includes at least two further transistors (Q3, Q4) than known types of amplifiers constituting a bipolar circuit using emitter coupled pairs. A further transistor (Q3, Q4) is serially connected to a respective emitter of an existing transistor (Q1, Q2) in the emitter coupled pair. The respective bases of the further transistors are cross-connected to the emitter of the existing transistor in the opposite leg of the pair. The amplifier may also be provided with a level shifting circuit and a matched level shift circuit (Q5, Q6, D1, D2).
Description
LINEARITY DIFFERENTIAL AMPLIFIER
The present invention relates to a linearity differential amplifier having a signal gain characteristic which is linear.
In the design of analogue circuits it is invariably necessary that
the information contained in the input signal should be linearly
transferred to the output of the circuit. To achieve this, the circuit
must have a linear transfer function.
A common analogue circuit is the differential amplifier and
therefore there is a need for linear differential amplifiers.
Accordingly an aim of the present is to provide an amplifier
with a small gain characteristic which is linear and independent of
device temperature.
According to the present invention there is provided a linearity
differential amplifier having a signal gain characteristic which is
linear, said amplifier comprising a plurality of transistors each
having a base collector and emitter, the base of a first transistor
receives an input signal, and the collector of the first transistor
generates an output signal and is connected to a first potential rail by
way of a first load, the emitter of the first transistor is connected to a
collector of a second transistor having its emitter connected to an
emitter load and a current source which is connected to a second
potential rail, a third transistor having its collector connected to the
first potential rail by way of a second load, its base connected to
earth and its emitter connected to the collector of a fourth transistor,
the emitter of the fourth transistor is connected to an emitter load
and a current source which is connected to the second potential rail, the base of the second transistor is connected the emitter of the third transistor and the collector of the fourth transistor, and the base of the fourth transistor is connected to the emitter of the first transistor and the collector of the second transistor.
The amplifier according to the invention has the advantages of independance of gain with temperature and collector current, and linear gain within the dynamic range of the amplifier when degeneration is used.
An embodiment of the present invention will know be described with reference to the accompanying drawings wherein:
Figure 1 shows an amplifier of known form having s degeneration,
Figure 2 shows an amplifier of known form having T degeneration,
Figure 3 shows a linearly differential amplifier according to the present invention,
Figure 4 shows a modification to the amplifier of Figure 3 to increase signal handling capability,
Figure 5 shows an example of a voltage transfer characteristic of an amplifier of known form, and,
Figure 6 shows an example of a voltage transfer characteristic of an amplifier according to the present invention.
Referring to Figures 1 and 2, the circuits shown are simple degenerated differential amplifiers which have a gain VO/Vin which equals the load RL/(RE + rel + re2) where re is the small signal emitter resistance, and RE the emitter load, and ren = (K.TY(q.1) where K is
Boltzmans constant, and q is the charge on an electron. From this it can be seen that the gain of the device is dependant on T (absolute temperature) and Ic (collector current), as such it is fundamentally non-linear. Increasing RE, the emitter load reduces these problems but also reduces the gain of the amplifier, therefore this technique is only of limited value in improving linearity.
The voltage transfer characteristic of such an amplifier having a degeneration of 250 is shown a Figure 5, where Vin is the input is the input voltage and V0 the output voltage.
To overcome these problems a circuit is required in which the gain is exactly equal to RL/RE (as opposed to RL/ (RE + rel + re2) if this could be achieved then the gain would be completely linear over the dynamic range of the circuit and independant of device temperature.
A circuit according to the present invention which achieves this result is shown in Figure 3.
The manner in which this circuit achieves this result can be described as follows:
Ten = AVben / Icons where AVben represents the change in (1)
base emitter voltage.
Inspection of the circuit then shows that; AVbel = AVbe3 (2) and AVbe2 = AVbe4 (3) also 1c1 = Ic3 = IC2 = Ic4 (4)
The gain of the circuit is given by:
g = RL/(RE = re1 + re2 + re3 + re4) (5)
However combining (1), and (5) gives::g = RL/(RE +Vbel/AIcl + Avbe2lAIc2 - AVbe31/Ic3 + AVbe4/tc) (6)
Therefore g = RL/(RE + #Vbe1/#Ic1 + #Vbe2/#Ic2 - #Vbe1/#Ic1 - #Vbe2/#Ic2) Simplifying g = RL/RE as required
The circuit shown in Figure 3 uses it degeneration, however it will readily be understood that T degeneration could be used.
Similarly, NPN forms of transistor are shown, whereas PNP could be used.
This circuit can be used to achieve very linear gain. However the dynamic range is limited by transistors Q3 and Q4 which will saturate if the input voltage exceeds approximately 0.6 Vpp. This can easily be overcome by placing a level shifting circuit between the emitter of Q1 and the base of Q4 and a matched level shift circuit is provided between the emitter of Q2 and the base of Q3.
Referring to Figure 4 a modification to the amplifier shown in
Figure 3 includes the provision of two further transistors Q5 and Q6 and diode D1 and D2 connected as shown. The signal handling capability of the amplifier is improved by the modification.
Alternatives will readily be seen by those skilled in the art, for example, diodes D1 and D2 may be replaced by a short circuit or by an equal number of series connected diodes. Diodes D1 and D2 may be replaced by resistors.
The voltage transfer characteristic of the improved differential amplifier having a degeneration of 250 is shown in Figure 6, where Vin is the input voltage and V0 the output voltage.
The invention as described applies to single ended input and output drive voltages. However the circuit according to the invention will work equally effectively with differential input and output, single ended input and differential output or differential input and single ended output.
With all the above combinations the output current can be used without converting to a voltage without affecting the performance of the circuit. This can be of advantage in many cases, e.g. input to translinear circuits, input to cascode circuits and input to mixers.
The invention can be used in any bipolar circuit (analogue or digital) that uses an emitter coupled pair, where noise performance is not of prime importance. The advantage of the invention can be obtained by simple substitution of this circuit into the position of the emitter coupled pair irrespective of the surrounding circuitry.
Claims (7)
1. A linearity differential amplifier having a signal gain characteristic which is linear, said amplifier comprising a plurality of transistors each having a base, collector and emitter, the base of a first transistor receives an input signal, and the collector of the first transistor generates an output signal and is connected to a first potential rail by way of a first load, the emitter of the first transistor is connected to a collector of a second transistor having its emitter connected to an emitter load and a current source which is connected to a second. potential rail, a third transistor having its collector connected to the first potential rail by way of a second load, its base connected to earth, and its emitter connected to the collector of a fourth transistor, the emitter of the fourth transistor is connected to an emitter load and a current source which is connected to the second potential rail, the base of the second transistor is connected the emitter of the third transistor and the collector of the fourth transistor, and the base of the fourth transistor is connected to the emitter of the first transistor and the collector of the second transistor.
2. A linearity differential amplifier as claimed in claim 1 in which 'T' degeneration is used.
3. A linearity differential amplifier as claimed in claim 1 in which liti degeneration is used.
4. A linearity differential amplifier as claimed in claims 2 or 3 wherein a level shifting circuit is provided between the emitter of the first transistor and the base of the fourth transistor.
5. A linearity differential amplifier as claimed in claim 4 wherein a matched level shift circuit is provided between the emitter of the second transistor and the base of the third transistor.
6. A linearity differential amplifier substantially as hereinbefore described.
7. A linearity differential amplifier substantially as hereinbefore described with reference to Figures 3, 4, and 6 of the accompanying drawings.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8723674A GB2211044A (en) | 1987-10-08 | 1987-10-08 | Linear differential amplifier |
| PCT/GB1988/000893 WO1989003612A1 (en) | 1987-10-08 | 1988-10-07 | Linearity differential amplifier |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8723674A GB2211044A (en) | 1987-10-08 | 1987-10-08 | Linear differential amplifier |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8723674D0 GB8723674D0 (en) | 1987-11-11 |
| GB2211044A true GB2211044A (en) | 1989-06-21 |
Family
ID=10625008
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8723674A Withdrawn GB2211044A (en) | 1987-10-08 | 1987-10-08 | Linear differential amplifier |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2211044A (en) |
| WO (1) | WO1989003612A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2677822A1 (en) * | 1991-06-17 | 1992-12-18 | Pioneer Electronic Corp | DIFFERENTIAL AMPLIFIER. |
| EP0669710A2 (en) * | 1994-02-24 | 1995-08-30 | Kabushiki Kaisha Toshiba | Variable gain amplifying circuit |
| EP1777603A1 (en) * | 2005-10-20 | 2007-04-25 | Honeywell Inc. | Voltage and current supply with compensation for power supply variations |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1230187B (en) * | 1989-04-28 | 1991-10-18 | Sgs Thomson Microelectronics | CIRCUIT DEVICE TO ELEVATE THE TRANSCONDUCTANCE OF A STAGE DIFFERENTIAL AMPLIFIER INCLUDING MOS TRANSISTORS. |
| US5136258A (en) * | 1989-04-28 | 1992-08-04 | Sgs-Thomson Microelectronics S.R.L. | Circuit arrangement for enhancing the transconductance of a differential amplifier stage comprising MOS transistors |
| US5113147A (en) * | 1990-09-26 | 1992-05-12 | Minnesota Mining And Manufacturing Company | Wide-band differential amplifier using gm-cancellation |
| FR2700083B1 (en) * | 1992-12-30 | 1995-02-24 | Gerard Perrot | Stable distortion amplifier for audio signals. |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1197453A (en) * | 1966-07-20 | 1970-07-08 | Losenhausen Maschinenbau Ag | Dynamic Balancing Machine |
| US4081758A (en) * | 1976-05-27 | 1978-03-28 | Rca Corporation | Low distortion signal amplifier arrangement |
| US4216436A (en) * | 1978-06-20 | 1980-08-05 | National Semiconductor Corporation | High gain differential amplifier |
| US4232270A (en) * | 1979-06-14 | 1980-11-04 | Rockwell International Corporation | High gain differential amplifier with positive feedback |
| GB2077542A (en) * | 1980-06-02 | 1981-12-16 | Philips Nv | Amplifier with negligible dc response |
| EP0046878A2 (en) * | 1980-08-30 | 1982-03-10 | TELEFUNKEN electronic GmbH | Feedback amplifier or threshold switch for a current-fed differential stage |
| EP0208365A1 (en) * | 1985-07-01 | 1987-01-14 | Koninklijke Philips Electronics N.V. | Voltage-current converter |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL6908784A (en) * | 1969-06-10 | 1970-12-14 | ||
| US4456887A (en) * | 1980-09-25 | 1984-06-26 | Pioneer Electronic Corporation | Differential amplifier |
| EP0161627B1 (en) * | 1984-05-16 | 1989-11-29 | Siemens Aktiengesellschaft | Bipolar amplifier circuit |
-
1987
- 1987-10-08 GB GB8723674A patent/GB2211044A/en not_active Withdrawn
-
1988
- 1988-10-07 WO PCT/GB1988/000893 patent/WO1989003612A1/en unknown
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1197453A (en) * | 1966-07-20 | 1970-07-08 | Losenhausen Maschinenbau Ag | Dynamic Balancing Machine |
| US4081758A (en) * | 1976-05-27 | 1978-03-28 | Rca Corporation | Low distortion signal amplifier arrangement |
| US4216436A (en) * | 1978-06-20 | 1980-08-05 | National Semiconductor Corporation | High gain differential amplifier |
| US4232270A (en) * | 1979-06-14 | 1980-11-04 | Rockwell International Corporation | High gain differential amplifier with positive feedback |
| GB2077542A (en) * | 1980-06-02 | 1981-12-16 | Philips Nv | Amplifier with negligible dc response |
| EP0046878A2 (en) * | 1980-08-30 | 1982-03-10 | TELEFUNKEN electronic GmbH | Feedback amplifier or threshold switch for a current-fed differential stage |
| EP0208365A1 (en) * | 1985-07-01 | 1987-01-14 | Koninklijke Philips Electronics N.V. | Voltage-current converter |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2677822A1 (en) * | 1991-06-17 | 1992-12-18 | Pioneer Electronic Corp | DIFFERENTIAL AMPLIFIER. |
| EP0669710A2 (en) * | 1994-02-24 | 1995-08-30 | Kabushiki Kaisha Toshiba | Variable gain amplifying circuit |
| EP0669710A3 (en) * | 1994-02-24 | 1997-06-11 | Toshiba Kk | Variable gain amplifying circuit. |
| EP1777603A1 (en) * | 2005-10-20 | 2007-04-25 | Honeywell Inc. | Voltage and current supply with compensation for power supply variations |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8723674D0 (en) | 1987-11-11 |
| WO1989003612A1 (en) | 1989-04-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |