CA2066705A1 - Instrumentation amplifier with automatic gain control - Google Patents
Instrumentation amplifier with automatic gain controlInfo
- Publication number
- CA2066705A1 CA2066705A1 CA 2066705 CA2066705A CA2066705A1 CA 2066705 A1 CA2066705 A1 CA 2066705A1 CA 2066705 CA2066705 CA 2066705 CA 2066705 A CA2066705 A CA 2066705A CA 2066705 A1 CA2066705 A1 CA 2066705A1
- Authority
- CA
- Canada
- Prior art keywords
- amplifier
- gain
- comparator
- output voltage
- resistor
- 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.)
- Abandoned
Links
- 238000005259 measurement Methods 0.000 claims abstract description 6
- 238000010276 construction Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/3005—Automatic control in amplifiers having semiconductor devices in amplifiers suitable for low-frequencies, e.g. audio amplifiers
- H03G3/3026—Automatic control in amplifiers having semiconductor devices in amplifiers suitable for low-frequencies, e.g. audio amplifiers the gain being discontinuously variable, e.g. controlled by switching
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Amplifiers (AREA)
- Indication And Recording Devices For Special Purposes And Tariff Metering Devices (AREA)
- Analogue/Digital Conversion (AREA)
- Control Of Amplification And Gain Control (AREA)
Abstract
This invention concerns an instrumentation amplifier capable of implemenating automatic control means for the gain of an amplifier (1), which can further be read as the value of the set gain in conjunction with the readout of the amplifier output voltage. The amplifier uses parallel feedback resistors (3) of which only one at a time is connected. The selection is performed on the basis of comparison of the output voltage against a reference voltage level (6, 7). An up/down counter is used to monitor the result of the comparison and to control a multiplexer (2) that connects the resistors (3) over the amplifier (1). The amplifier is best suited to measurements in which multiple low-cost amplifiers must be used and the amplitude of the incoming analog signal varies by several orders of magnitude.
Description
h~ U U U ~ U V
--~W091/05406 PCT/FI90/00226 Instrumentation amplifier with automatic gain control The preqent invention relates to an instrumentation a~pli-fier of a type in accordance with the preamble of claim 1 An instrumentation amplifier is by definition a device intended for the measurement of analog signals, often a~ a low level, from different types of Qensors The amplifier is conventionally constructed using a few operational ampli-fiers, but it can also ~e built around amplifying stages designed around UJT and FET devices The output signal o - ;
the instrumentation amplifier is generally read via an -analog-to-digital converter connected to a co~puter that can convert an output ~ignal range 0 5 v of the amplifier irto a corre~ponding digital signal with a Ycale of 0 1023 In ~ -certain application the measurement ~ignal level can vary widely, o g , from 10 millivoltq to 5 volts which means a span of three orderQ of magnitude If the analog-to-digital 20 converter connected to the computer ha~ a meagurement rang- - -of 0 5 V, the lower end of the measurement range has insufficient measurement re~olution $he-converter of the exemplifying ca~e with a resolution of 1 1000 ig already in~ufficient for mea3urement of millivolt-level ~ignals at-any accuracy, although the inherent reQolution limit of most analog Jignal~ is in the order of 0 1 percent In the art the practical Jolution to the problem i9 the so-called logar~thmic amplifi-r, who~e~output signal corsesponds logar~thmically to the input signal A dsawback to thi~
appsoach ~9 that the logasithmic amplifier mu~t be i~pl~m nt-d u~ing a foswasd-biased diode, which i_ a mo~t t-~p-raturo-~ena~tiv component The thermal drift of the a~plifi-r mu~t be compon~ated in on way or another with the - h lp of, e g , a t mporature-d pendent re_istor alQo called a th rmi~tor The pract}cal i~plementationQ of a logasithmic . , .
WO91/05406 ~ 6 ~ 7 o ~ PCT/FIgO/00226 :-amplifier tend to be complicated and costly. The feasibilityof application~ requiring a multitude of qen~ors can thuq easily be limited by cost factors.
It is an object of the pr~sent invention to develop a simpls and cost-effective instrumentation amplifier, which is capable of measuring the analog output signal~ of sensors at a sufficient accuracy even if the signal amplitude may vary in a range of several orders of magnitude.
~he principal advantages of the invention lie in its low cost, which results from the use of basic components.
Amplifiers in accordance with the invention avoid the large temperature dependence of logarithmic amplifiers so l~ difficult to compensate.
, "' In order to implement the above-described function, the invention i~ principally characterized by what is stated in ~;
the diqclosed claims. -;
Figure l shows the operating principle and a pO8 qible practical implementation of the amplifier at the component level. - -In accordance with the invention, the instrumentation ampli-fier ~hown in Fig. l is implemented by a design which makes the amplifier to perform an automatic gain control until it~
output ignal i~ alway~ in a range of, e.g., l...lO V. The amplifior i~ capable of measuring a voltage span extending ~-from, .g., one millivolt to ten voltQ practically at the Jame accuracy. The amplifier can be constructed u ing simplo baJ~c component , which avoid~ the large thermal drift so difficult to eompenaato in a logarithmic amplifier. The amplifier l is providod with a feedback networX comprising a rultiploxer 2 and resistors 3 ~o that one resi3tor at a time ""','' " :, ~091/05406 PCT/F190/00226 is connected ~rom the amplifier output to the input. The multiplexer is controlled via control lineg 4. The control lines are driven by an up/down counter 5. ~he output voltage of the amplifier is compared against a l V reference voltage ~ wit~ the help of a comparator 6. If the output voltage is below l v, the comparator output goes to logic l state and the counter is incremented. The output lines 4 of the counter 5 control the multiplexer 2 making it change its channel, whereby a feedback resistor 3 of larqer value is 1~ selected. Due to the heavy feedback, the output of the amplifie- is always held above l V. The gain of the amplifier can be read by a computer from the states of the output lines o~ the counter 5.
The above-described Qimple embodiment of the invention is most elementary; therefore, it should be underQtood not to limit the scope of the invention that permits variations within the di~closed patent claims. In practical de3igns the amplifier construction can be implemented with the help of several different component alternatives. For instance, the multiplexer can be replaced by other types of logic circuits.
, "., . , .
, ~
--~W091/05406 PCT/FI90/00226 Instrumentation amplifier with automatic gain control The preqent invention relates to an instrumentation a~pli-fier of a type in accordance with the preamble of claim 1 An instrumentation amplifier is by definition a device intended for the measurement of analog signals, often a~ a low level, from different types of Qensors The amplifier is conventionally constructed using a few operational ampli-fiers, but it can also ~e built around amplifying stages designed around UJT and FET devices The output signal o - ;
the instrumentation amplifier is generally read via an -analog-to-digital converter connected to a co~puter that can convert an output ~ignal range 0 5 v of the amplifier irto a corre~ponding digital signal with a Ycale of 0 1023 In ~ -certain application the measurement ~ignal level can vary widely, o g , from 10 millivoltq to 5 volts which means a span of three orderQ of magnitude If the analog-to-digital 20 converter connected to the computer ha~ a meagurement rang- - -of 0 5 V, the lower end of the measurement range has insufficient measurement re~olution $he-converter of the exemplifying ca~e with a resolution of 1 1000 ig already in~ufficient for mea3urement of millivolt-level ~ignals at-any accuracy, although the inherent reQolution limit of most analog Jignal~ is in the order of 0 1 percent In the art the practical Jolution to the problem i9 the so-called logar~thmic amplifi-r, who~e~output signal corsesponds logar~thmically to the input signal A dsawback to thi~
appsoach ~9 that the logasithmic amplifier mu~t be i~pl~m nt-d u~ing a foswasd-biased diode, which i_ a mo~t t-~p-raturo-~ena~tiv component The thermal drift of the a~plifi-r mu~t be compon~ated in on way or another with the - h lp of, e g , a t mporature-d pendent re_istor alQo called a th rmi~tor The pract}cal i~plementationQ of a logasithmic . , .
WO91/05406 ~ 6 ~ 7 o ~ PCT/FIgO/00226 :-amplifier tend to be complicated and costly. The feasibilityof application~ requiring a multitude of qen~ors can thuq easily be limited by cost factors.
It is an object of the pr~sent invention to develop a simpls and cost-effective instrumentation amplifier, which is capable of measuring the analog output signal~ of sensors at a sufficient accuracy even if the signal amplitude may vary in a range of several orders of magnitude.
~he principal advantages of the invention lie in its low cost, which results from the use of basic components.
Amplifiers in accordance with the invention avoid the large temperature dependence of logarithmic amplifiers so l~ difficult to compensate.
, "' In order to implement the above-described function, the invention i~ principally characterized by what is stated in ~;
the diqclosed claims. -;
Figure l shows the operating principle and a pO8 qible practical implementation of the amplifier at the component level. - -In accordance with the invention, the instrumentation ampli-fier ~hown in Fig. l is implemented by a design which makes the amplifier to perform an automatic gain control until it~
output ignal i~ alway~ in a range of, e.g., l...lO V. The amplifior i~ capable of measuring a voltage span extending ~-from, .g., one millivolt to ten voltQ practically at the Jame accuracy. The amplifier can be constructed u ing simplo baJ~c component , which avoid~ the large thermal drift so difficult to eompenaato in a logarithmic amplifier. The amplifier l is providod with a feedback networX comprising a rultiploxer 2 and resistors 3 ~o that one resi3tor at a time ""','' " :, ~091/05406 PCT/F190/00226 is connected ~rom the amplifier output to the input. The multiplexer is controlled via control lineg 4. The control lines are driven by an up/down counter 5. ~he output voltage of the amplifier is compared against a l V reference voltage ~ wit~ the help of a comparator 6. If the output voltage is below l v, the comparator output goes to logic l state and the counter is incremented. The output lines 4 of the counter 5 control the multiplexer 2 making it change its channel, whereby a feedback resistor 3 of larqer value is 1~ selected. Due to the heavy feedback, the output of the amplifie- is always held above l V. The gain of the amplifier can be read by a computer from the states of the output lines o~ the counter 5.
The above-described Qimple embodiment of the invention is most elementary; therefore, it should be underQtood not to limit the scope of the invention that permits variations within the di~closed patent claims. In practical de3igns the amplifier construction can be implemented with the help of several different component alternatives. For instance, the multiplexer can be replaced by other types of logic circuits.
, "., . , .
, ~
Claims (2)
1. An instrumentation amplifier with automatic gain control, said amplifier comprising a feedback network incorporating parallel resistors (3), of which one at a time is connected to set the amplifier gain through a comparison of the output signal level to a reference voltage (7) so many times with a subsequent change of feedback resistor (3) as is necessary to make the measurement signal from the amplifier to exceed a set reference voltage, and simultaneously with the read operation of the amplified signal, the gain is read from the value of the resistor (3) selected, c h a r a c t e r -i z e d in that the parallel feedback resistors (3), which define the gain of the amplifier (1), are connected via a multiplexer (2) or a logic circuit whose control (4) takes place by an up/down counter (5) that further monitors the state of a comparator (6) until it detects the signal to have exceeded the reference voltage level, whereby the comparator stops the counter (5) and latches the value of the feedback resistor, after which the output voltage of the amplifier (1) is read, together with the selected gain, that is, the value of the resistor (3) selected by the state of the output lines of the up/down counter (5).
2. An amplifier in accordance with claim 1, c h a r a c -t e r i z e d in that, in parallel with the comparator (6), there is connected another upper limit comparator referenced to the maximum level of the amplifier output voltage and that the second comparator decrements the up/down counter in the opposite direction if the output voltage of the amplifier tends to increase excessively high.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI894591A FI87861C (en) | 1989-09-28 | 1989-09-28 | An automatic amplification control instrumentation amplifier |
| FI894591 | 1989-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2066705A1 true CA2066705A1 (en) | 1991-03-29 |
Family
ID=8529071
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2066705 Abandoned CA2066705A1 (en) | 1989-09-28 | 1990-09-26 | Instrumentation amplifier with automatic gain control |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0494198A1 (en) |
| JP (1) | JPH05500590A (en) |
| CA (1) | CA2066705A1 (en) |
| FI (1) | FI87861C (en) |
| WO (1) | WO1991005406A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5886017A (en) * | 1986-06-11 | 1999-03-23 | Procyon Pharmaceuticals, Inc. | Protein kinase C modulators. E. |
| FR2702581B1 (en) * | 1993-03-12 | 1995-06-02 | Sagem | Multiplier circuit with potentiometers and electric energy meter incorporating such a circuit. |
| DE102019113360A1 (en) * | 2019-05-20 | 2020-11-26 | Carl Zeiss Microscopy Gmbh | Lighting device for a light microscope and lighting method |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2853642A1 (en) * | 1978-12-09 | 1980-06-12 | Biotronik Mess & Therapieg | AMPLITUDE CONTROL UNIT FOR ECG SIGNALS |
| US4739307A (en) * | 1984-01-31 | 1988-04-19 | Analogic Corporation | Multichannel predictive gain amplifier system |
| US4553104A (en) * | 1984-03-01 | 1985-11-12 | Honeywell Inc. | Method of compensating an amplifier system having a variable gain amplifier to achieve a constant overall system signal gain and an apparatus utilizing the same |
| FR2592537B1 (en) * | 1985-12-30 | 1991-05-31 | Inst Francais Du Petrole | DEVICE FOR THE AMPLIFICATION AND SAMPLING OF MULTIPLEX ANALOG SIGNALS. |
-
1989
- 1989-09-28 FI FI894591A patent/FI87861C/en not_active IP Right Cessation
-
1990
- 1990-09-26 WO PCT/FI1990/000226 patent/WO1991005406A1/en not_active Application Discontinuation
- 1990-09-26 JP JP51327790A patent/JPH05500590A/en active Pending
- 1990-09-26 EP EP19900914180 patent/EP0494198A1/en not_active Withdrawn
- 1990-09-26 CA CA 2066705 patent/CA2066705A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0494198A1 (en) | 1992-07-15 |
| FI87861C (en) | 1993-02-25 |
| FI87861B (en) | 1992-11-13 |
| FI894591A0 (en) | 1989-09-28 |
| JPH05500590A (en) | 1993-02-04 |
| FI894591A (en) | 1991-03-29 |
| WO1991005406A1 (en) | 1991-04-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |