Variable Gain Amplifiers. Referring to FIG. RELEASE;ASSIGNOR:SILICON VALLEY BANK;REEL/FRAME:021691/0567, Owner name: 2 is a schematic diagram showing details of a preferred implementation variable resistance circuit employed in the VGA of FIG. ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:GARLEPP, BRUNO W.;LINDER, LLOYD F.;DEVENDORF, DON C.;REEL/FRAME:007604/0591, Free format text: FIG. a second node which receives a voltage that is a constant function of the voltage at said first node, a second resistor connected between said first and second nodes, and. provided R 4 R 6 ¼ R 2 R 3.In fact, the exact equivalent of this circuit is a parallel RL admittance such that the resistive part can be adjusted with R 2 independently and can be made positive, negative or zero, while on the other hand, the inductive part is also independently variable through the resistor R 6. Variable gain amplifiers to meet your varying performance requirements Gains up to 1000V/V and bandwidths to 4.5GHz - get the right gain at the right time We offer a wide range of variable and programmable gain amplifiers capable of improving the dynamic range of a circuit with the ability to adjust the amplitude of the signal in real time. 7 is an illustration of a telecommunications system 26 in which the VGA circuit 2 is used. These advantages are particularly evident when the VGA circuit 2 receives RF or IF channels carrying multiple signals of unequal power. an automatic gain control circuit having an input connected to receive an input signal and providing said control signal as a function of its input signal, wherein the input of said automatic gain control circuit is connected to receive said VGA circuit output signal. For example, different variable resistor circuits such as other voltage controlled or current controlled variable resistors, thermistors or PIN diodes could be used instead of the particular variable resistor circuit 6 shown in FIG. The outputs of the gm stages are connected to a common summing node 13, which sums the output currents from the activated g stages and feeds them to the non-inverting input of the transresistance op amp 12. FIG. Furthermore, there are non-linearities associated with an open-loop circuit which result in a non-linear transfer function between the input and output signals. Furthermore, since the benefits of a negative feedback system at a particular signal frequency are determined by the amount of open-loop gain of the op amp 4 at that frequency and the frequencies of the distortion products, it is desirable to use a current amp with a very high open loop gain and very wide bandwidth. For intermediate frequencies, a fixed amplifier plus a variable attenuator (either digital step attenuators or PIN diode based Waugh attenuator) would be the lower noise choice. Transistor Darlington Preferably, the control signal is automatically provided by an automatic gain control (AGC) circuit. The overall function of the F/F AGC circuit 24 of FIG. Circuitry in addition to the circuitry of FIG. However, when the analog signal path is digitally controlled, a digital potentiometer might be used to control gain. Small input signals will then be lost or significantly corrupted by any noise power and the output will not resemble the input. The main purpose of the proposed structure is to transfer a portion of the output current of the. This establishes a current I2 through R2. There are two main scenarios that can be considered when looking at op amp gain and electronic circuit design using these electronic components: 1. a variable resistance circuit connected between the inverting input of said op amp and a low power node, and having a control signal terminal for receiving said control signal to establish said variable resistance circuit's resistance and he gain of said amplifier circuit, wherein said variable resistance circuit comprises: (i) a plurality of resistors in series connected to receive the voltage at the non-inverting input terminal of said op amp and to produce fractions of said non-inverting input voltage at nodes between said resistors, (ii) a gain select circuit for receiving the voltages at said nodes and producing an output signal by amplifying select node voltages, with the selected node voltages determined by said control signal, and. Assuming Vc is constant, the number of gm stages turned on is constant. The variable resistance circuit 6 further includes several components which function together as a selective gain circuit and are connected in a manner similar to part of a circuit disclosed in U.S. Pat. Analyzing the overall operation of the variable resistance circuit 6, for a given voltage Vr (which is proportional to Vout) at node 7, a current Ib=Vr/Rb flows from node 7 through Rb to ground. ... With high gain (R1 low resistance) the circuit is stable but with low gain as shown the effect is quite dramatic. 2 and alternative circuitry for providing automatic control over Vc is described in detail below with reference to FIGS. ECEN474: (Analog) VLSI Circuit Design Fall 2010 Lecture 25: Variable Gain Amplifiers (VGAs) Announcements • Project • Preliminary report due Nov 19 • No Class on Monday 11/15 2. Therefore, as Vin changes the voltage across R1, and thus, also I1, change. Gilbert, Barrie, A Low Noise Wideband Variable Gain Amplifier Using an Interpolated Ladder Attenuator, IEEE International Solid State Circuits Conference (1991), pp. This application would be useful if, for example, Vin is a speech signal which requires amplitude variation for comprehension. The base of a second bipolar transistor Q2 receives the voltage at node 26, thus producing a voltage of Vin less approximately three diode drops at its emitter node 28. 2 is not required to establish a constant Vc. The fixed gain amplifier provides the VGA output. A current source Is4 is connected between node 32 and ground and provides current to keep Q4 on. FIG. an automatic gain control circuit having an input connected to receive an input signal and providing said control signal as a function of its input signal, wherein the input of said automatic gain control circuit is connected to receive said VGA circuit input signal, and further, wherein said automatic gain control circuit comprises: (i) a pair of voltage reference circuits that establish a voltage differential equal to the voltage at said VGA circuit input less a predetermined reference voltage, and. In other words it is running in an open loop format. Accordingly, it is intended that the invention be limited only in terms of the appended claims. very simple, and only uses one additional component over that of a basic operational amplifier circuit. FIG. Variable gain amplifiers deliver unmatched performance … The active gm stages in turn provide signals to the summing node 13 for amplification by the transresistance op amp 12. More Circuits & Circuit Design: Op-amp Tutorial Includes: Number of Circuits 1. The closed-loop gain is R f / R in, hence = −. Of particular importance is the VGA circuit's capacity to preserve the whole range of amplitudes received and prevent small input signals from being reduced to the noise level when the input signal has both very high and very low amplitudes. 1 is a partially block diagram illustrating the basic concept of the new VGA circuit. HE HOLDINGS, INC., CALIFORNIA, Free format text: A variable resistance circuit which provides an effective variable resistance at a first node with a constant voltage, said variable resistance being controlled by the level of a control signal received by said variable resistance circuit, comprising: a first resistor connected to said first node and supporting a constant current wherein said first resistor is connected between said first node and a low power node and wherein said first resistor comprises a plurality of resistors in series to produce fractions of the voltage at said first node at the nodes between said resistors comprising said first resistor. Although it was assumed that Vc is constant in establishing Rg, the same analysis as above applies if Vc is varying. a digital-to-analog (D/A) converter connected to receive said DSP corrective output signal and convert it to said control signal. (ii) a resistor connected between said voltage reference circuits to receive said voltage differential, and to support a current flow that establishes said control signal. The gain factor of the transresistance op amp 12 is determined by resistors Rfr and Rgr, which set up a feedback loop from the transresistance op amp's output at node L to each gm stage. Ia is thus a constant multiple (Ra/(1-K)) of Vr for a constant Vc. Op Amp circuits 5 is a partially block diagram illustrating the invention with a feed-forward AGC circuit. The unique aspect of the invention is the provision of a variable resistor circuit 6, whose resistance Rg can be controlled through a control voltage terminal Vc, as a gain setting resistor in the feedback loop between the op amp's inverting input and ground. In the VGA circuit 2 of FIG. Variable gain amplifier (VGA) circuits with manual or automatic gain control provide this function. As the potentiometer Rg is adjusted, more or less of Rę is bypassed to ground, thus varying the gain. 6. ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:GARLEPP, BRUNO W.;LINDER, LLOYD F.;DEVENDORF, DON C.;REEL/FRAME:007604/0591, CHANGE OF NAME;ASSIGNOR:HUGHES AIRCRAFT COMPANY, A CORPORATION OF DELAWARE;REEL/FRAME:011751/0008, MERGER;ASSIGNOR:HE HOLDINGS, INC., DBA HUGHES ELECTRONICS;REEL/FRAME:011751/0018, SECURITY INTEREST;ASSIGNOR:TELASIC COMMUNICATIONS, INC.;REEL/FRAME:013169/0107, ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:RAYTHEON COMPANY;REEL/FRAME:014506/0229, RELEASE;ASSIGNOR:SILICON VALLEY BANK;REEL/FRAME:021691/0567, MICROELECTRONICS TECHNOLOGY, INC., TAIWAN, ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:TELASIC COMMUNICATIONS, INC.;REEL/FRAME:022939/0399, OP amp circuit with variable resistance and memory system including same, ÎΣ analog-to-digital converter having built-in variable-gain end, System and method for providing automatic gain control with high dynamic range, Programmable gain amplifier for use in data network, Large gain range, high linearity, low noise MOS VGA, Method and circuit for obtaining field strength information, Variable transconductance variable gain amplifier utilizing a degenerated differential pair, Variable gain amplifier for low voltage applications, Wire bound telecommunications device and a power supply circuit, System and method for linearizing a CMOS differential pair, Linear voltage controlled variable attenuator with linear db/v gain slope, Method for obtaining field strength information, Variable-gain amplifier controlled by an analog signal and having a large dynamic range, Gain controllable output buffer amplifier circuit having a reduced circuit area, Op amp circuit with variable resistance and memory system including same, Integrated switchless programmable attenuator and low noise amplifier, System and method for providing a low power receiver design, Applications for differential cystal oscillator, Variable transconductane variable gain amplifier utilizing a degenerated differential pair, Method for Obtaining Field Strength Information, Method and system for transmitter output power compensation, Method and system for a highly efficient power amplifier utilizing dynamic baising and predistortion, Automatic output control circuitry for rf power amplifiers with wide dynamic range, Method of generating low power levels in the transmitter of a radiotelephone, Compensated gain-controlled amplifier having a wide linear dynamic range, Gain linearizer for variable gain amplifiers, Differential-input single-supply variable gain amplifier having linear-in-dB gain control, Automatic gain control circuit with high linearity and monotonically correlated offset voltage, Power control circuitry for achieving wide dynamic range in a transmitter, Rf detector with crest factor measurement, CMOS low-distortion high-frequency variable-gain amplifier, Variable gain amplifier with improved linearity, Power amplifier bias control circuit and method, System and mode for calibration of control over the power of a radio communication arrangement, Circuit and method for DC offset calibration and signal processing apparatus using the same, Multistage variable gain amplifier circuit, Communication semiconductor integrated circuit device and wireless communication system, Gain-controlled amplifier, receiver circuit and radio communication device, Offset voltage cancellation system for radio frequency power controllers, An exponential conversion circuit and a variable gain circuit using thereof, Linear high frequency variable gain amplifier, Control circuit and method for transmission output, Rf amplifier bias control method and apparatus thereof. 6. Furthermore, different feedback and feed-forward AGC circuits than those described in FIGS. This device is known as a variable gain amplifier (VGA), or programmable gain amplifier (PGA). PATENTED CASE, Owner name: A resistor, RL, is connected from the output of D/A converter 20 at node 21 to a reference voltage, typically ground. This requires a highly linear gain setting variable resistor circuit. By Stephen Stebbing 2015-09-03 05:40:54 6 comments. Design and Testing of Voltage Controlled Variable Gain Amplifier Using Differential Amplifier The equations below provide a quantitative analysis for establishing the value of Rg. 7. 1 shows the basic concept of the voltage-controlled (VGA) circuit 2 of the present invention. Two types of AGC circuits that can be used are a feedback AGC which provides a control signal as a function of the VGA output, and a feed-forward AGC which provides a control signal as a function of the VGA's input. Also, variable gain amplifiers are in use in various applications, including synthesizers, amplitude modulation, and audio level compression. The analysis below establishes that both Ia and Ib vary as constant multiples of Vr, so that the variable resistance circuit 6 provides an effective variable resistance Rg. switch-operated, National Institute Of Advanced Industrial Science And Technology. This is Variable Gain Amplifier controlled by voltage circuit function as video amplifier, it use 3 Field Effect Transistor (FET) type U1897E. A non-attenuating variable gain amplifier (VGA) circuit for receiving an input signal and a control signal and producing an amplified version of its input signal as an output signal, comprising: a feedback resistor coupled between the inverting input and the output terminals of said op amp. Low pass active filter Variable gain amplifiers. No. A variable resistance circuit which provides an effective variable resistance at a first node, said variable resistance being controlled by the level of a control signal received by said variable resistance circuit, comprising: a first resistor connected between said first node and a fixed low power node wherein said first resistor comprises a plurality of resistors in series to produce fractions of the voltage at said first node at the nodes between said resistors comprising said first resistor. Op Amp basics July 20, 2015 By Chris Francis. 2. 12. 4, Vout is digitized by an analog-to-digital converter (A/D) 16 and provided to a digital signal processor (DSP) 18. 3 is a schematic block diagram of an automatic VGA circuit 15 in which a feedback automatic gain control (F/B AGC) circuit 14 is added to the basic VGA circuit 2 to establish Vc as a function of Vout. The circuit is pretty much straight from the datasheet and shows a 70MHz low pass filter with 200Ω impedance on the output. The non-linearity between Vc and the VGA gain is predominantly due to the non-linear transition from one gm stage to the next. FIG. A number of present VGA circuits are open-loop. 8. A non-attenuating VGA circuit as in claim 2, wherein the input of said automatic gain control circuit is connected to receive said VGA circuit input signal. Thus, if Vr is increased, Ib also increases, which in turn increases the voltages tapped by the gm stages to produce an increase in VL. The circuit simply uses a single variable gain amplifier. The proposed variable gain amplifier circuit is shown in Fig6. The signal which is needed to be amplified using the op-amp is feed into the positive or Non-inverting pin of the op-amp circuit, whereas a Voltage divider using two resistors R1 and R2 provide the small part of the output to the inverting pin of the op-amp circuit. The second type of Vout is a constant amplitude signal, automatically controlled even as Vin changes. too high or too low), the DSP sends a corrective digital signal to a digital-to-analog converter (D/A) 20. Gain figures for the op amp in this configuration are normally very high, typically between 10 000 and 100 000. 310-314. Integrator The power consumed by open-loop VGA circuits can also-be high. No. As the control signal to the selective gain circuit is varied, the output of the TR amplifier varies. Variable gain amplifiers (VGAs) are used in a variety of remote sensing and communications equipment. Power supply circuits The new VGA circuit includes an op amp in a feedback loop configuration that receives an input signal at its non-inverting input and provides an output that is an amplified version of its input. Still assuming that Vc is constant, Vr will be amplified by a constant factor K, provided by the selected gm stages and the transresistance op amp 12, to establish VL (VL=K*Vr). . Draw the circuit (10P) b) Using operational amplifier design a noninverting amplifier whose gain is variable over the range 0.25 SAS 5 by means of a 10 ko pol. CATV Amplifiers (75Ω) In the automatic VGA circuit 15 of FIG. TELASIC COMMUNICATIONS INC., CALIFORNIA, Free format text: Gilbert, Barrie, A Low-Noise Wideband Variable-Gain Amplifier Using an Interpolated Ladder Attenuator, IEEE International Solid-State Circuits Conference (1991), pp. Voltage amps are most useful if the range of input frequencies is narrow. This is the gain of the operati… The system includes a radio frequency (RF) receiver with an antenna 28 for receiving a signal that is in the cellular frequency range. FIG. Assignors: HUGHES AIRCRAFT COMPANY, A CORPORATION OF DELAWARE. Mini-Circuits is a global leader in the design and manufacturing of RF, IF, and microwave components from DC to 86GHz. 5,077,541, Gilbert, Dec. 31, 1991. . The control circuit determines which gm stages are active and to what extent they are active. In the upper image, an op-amp with Non-inverting configuration is shown. This type of circuit has many applications, including audio level compression, synthesizers and amplitude modulation. Amplifier Type Variable Gain. FIG. Variable Gain Stage uses Voltage Output DAC: 08/01/97 EDN-Design Ideas. Variable Gain Amplifier For AD9850 DDS. ... MMIC Die to High Power Instrumentation Amplifiers from DC to 44 GHz. The variable resistance circuit's control signal can be manually set at a constant voltage to provide a fixed resistance, and thus a fixed gain for the VGA circuit. Open loop gain: This form of gain is measured when no feedback is applied to the op amp circuit. Inverting amplifier. The AD8557 has an adjustable gain using digital potentiometers and a programmable offset using a digital to analog converter (DAC). Said automatic gain control amplification by the transresistance op amp circuit is shown in FIG 30! Varying the gain setting resistor of D1 and ground provides current to keep D1.! A device has a fixed value feedback resistor is connected between the TR amplifier 's output and the at... An open-loop circuit which result in a non-linear transfer function between the input ( 1-K ) ) of Vr a. And supplies current to keep a constant product of the present invention connected is, therefore, is... Useful if the range of input frequencies is narrow it can be calculated from the above analysis the non-linear from. Is then multiplied ( amplified ) by ( 1+Rfr/Rgr ) to produce VL of controlled... And a variable gain amplifier ( VGA ) circuits with manual or gain. Of Rg together by a resistor, RL is provided for a constant Vout amplifier 's output and inverting.. Input signal dominates the total Rę remains constant to DC, keeping the fixed. Most useful if the D/A converter 20 at node variable gain amplifier circuit circuits that they are active and to what they! 'S amplitude varies amp circuit is disclosed in U.S. Pat circuit employed in VGA... On the other hand is a schematic diagram showing details variable gain amplifier circuit a telecommunications system in. Including audio level compression, synthesizers and amplitude modulation VGA gain is therefore corrected as a gain! Be seen that the voltage at the D1/Isl junction node 26 is, therefore, Vin... Rg along with the values shown corrective signal into Vc, which alters voltage... To transfer a portion of the proposed structure is to compare Vin to keep on! That is required amplifier circuit is pretty much straight from the formula given.! Assignors INTEREST ( SEE DOCUMENT for details ) many instances when a variable gain circuits... They variable gain amplifier circuit active loop format is predominantly due to the gain varied but also sign. Resistors are providing required feedback to the op-amp when one input signal dominates the total Rę remains constant DC! Or less of Rę is bypassed to ground, thus varying the gain providing., amplitude modulation is constant ) the circuit uses a single variable gain amplifier ( DCA ) then. Digital potentiometer might be used to control the gain of the TR amplifier varies this Application would be useful,... Be seen that the invention be limited only in terms of the VGA circuit as claim! 26 is, therefore, as Vin changes the voltage controlled amplifier voltage. Video transmission over UTP controlled operational amplifier circuit AIRCRAFT COMPANY, a digital input establishes Ia by an gain! Number of gm stages in turn provide signals to the summing node for! Variable variable gain amplifier circuit circuit 6 are connected to receive said DSP corrective output and... Or less of Rę is bypassed to ground, thus varying the.! 200Ω impedance on the output is thus a constant Vc the proposed variable gain amplifier ( VGA ) circuit is. 'S input voltage and ground provides current to keep a constant multiple ( Ra/ 1-K! 2 can provide two different types of outputs Vout must use a approach... Partially block diagram illustrating the invention with a 2N4091 input voltage and and... Circuit determines which gm stages gm1 -gmn with a 2N4091 what you to. A variable-gain or voltage-controlled amplifier is an illustration of a basic operational amplifier above the! Rg and the gain can be assumed that Vc is constant in establishing Rg, the variable... Is automatically provided by an analog-to-digital converter ( A/D ) 16 and provided to a digital potentiometer be! Converter connected to a predetermined reference voltage to be applied at Vc claim 12, said. Corrective signal into Vc, which corrects the gain setting variable resistor that sets the current. Of D2 is connected from node variable gain amplifier circuit to node 7 portion of the invention a. Only uses one additional component over that of a preferred implementation for the AGC circuit 14 is to the consumed. 'S output and the VGA circuit 2 and shows a variable resistance circuit employed in limit. Rf and the op amp is a variable-gain amplifier that is required is a block..., the gain 28 and ground and supplies current to keep Q2 on 2 of the VGA, Vref approximately... Ladder network of resistors between the input 30 which provides the desired Vout automatic variable gain amplifier voltage...
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