CS214346B1 - Circuit of amplifier with changeable amplification with possibility of amplification polarity switching-over - Google Patents

Description

A more suitable element for switching the feedback resistors of the amplifier is an electromechanical switch - relay. However, this solution usually exhibits low mechanical reliability and low switching speed, and in some cases, as in the first case, contact bouncing during switching is defective.

Therefore, electronic, usually semiconductor switches, have been increasingly used for this purpose lately. Most wiring of these switchable amplifiers is based on direct replacement of the mechanical switch with an electronic switch. However, this results in unfavorable real properties of the electronic switches, especially the resistance of the switch in the closed state and the dependence of this resistance on the applied voltage and the ambient temperature.

Switchable amplifier circuits are also known in which the influence of unfavorable real properties of the switches is suppressed by a suitable circuit arrangement. However, the wiring usually includes two operational amplifiers and does not allow switching the gain polarity simultaneously.

These drawbacks are largely eliminated by switching the amplifier with a switchable gain amplifier according to the invention, the principle being that a series combination of at least three resistors is connected between the input input and the common conductor, with switches that are individually connected between the series resistor. its other end connected to the non-inverting input of the opamp.

The advantage of connecting a switchable gain amplifier with the possibility of switching the polarity of the gain according to the invention is that it is almost free from the influence of the unfavorable properties of the electronic switches. The final resistance of the closed switch, on the order of several hundred ohms, forms with the input resistance of the connected operational amplifier, on the order of tens of gigaohms, a divider with a dividing ratio approaching fractions per mille of one. Therefore, the final resistance of the closed switch and its changes depending on the applied voltage, resp. they do not have a significant effect on the length of the circuit.

The connection of the amplifier with switchable gain with the possibility of switching the gain polarity is shown in the drawing.

The amplifier circuit according to the invention is provided with an input 1 and an output 2 and comprises an operational amplifier 4 with an inverting input 5, a non-inverting input 6 and an output 7. The circuit comprises at least two switches 14 and 15 each supported by control input 16 and control circuit 8 s. at least two outputs 9 which are connected to their respective control inputs 16 of the individual switches 14 and 15. It further comprises an input resistor 17, a grounded resistor 19, a feedback resistor 18, a series combination 13 of at least three resistors 10, 11, 12 and a common conductor 3.

An input resistor 17 is connected between the wiring input 1 and the inverting input 5 of the operational amplifier 4. A feedback resistor 18 is connected between the inverting input 5 of the operational amplifier 4 and the output 7 of the operational amplifier 4. A grounded resistor 19 is connected between the inverting input 5 and the common wire. The output 7 of the operational amplifier 4 is simultaneously the output 2 of the entire wiring.

A series combination of at least three of 3 is connected between the input 1 of the wiring and the common wire 3

The points at which the individual resistors 10, 11, 12 of the series combination 13 are connected to each other are individually connected via switches 14 and 15 to the non-inverting input 6 of the operational amplifier 4.

It is characteristic of a switchable gain amplifier with the possibility of switching the gain polarity according to the invention that only one switch 14, 15 is closed at all times and all other switches 14, 15 are open. The switching of the individual switches takes place by electrical signals from the outputs 9 of the control circuit 8, which are applied to the control inputs 16 of the switches 14 and 15.

In the case that the nth switch 14, 15 is closed, where n stands for the sequence number of switches 14, 15, and the other switches 14, 15 are open, we get at the output 2 the voltage connection given by the relation.

N

n = 0 wherein Uj represents the input voltage of the amplifier, with _two of its output voltage, R₁ input resistor 17, _R2, a feedback resistor 18, R uzemněrfý resistor 19, R _ln nth resistance of the series combination 13 of resistor 12 »ϋ '. 12 »Bjy V th resistor from series combination 13 of resistors 10, 11, 12, where ni 1 / denotes sequence number of resistors 10, 11, 12 of series combination 13 counted from input 1 wiring and simultaneously n for η« 1, indicates closed switch 14 , 15.

If, for example, we select R ^ · · R / m, R ₂ - R, R ^ R R // m - 1 /, where R denotes the chosen resistance value m and the maximum required absolute value of the gain and further denotes n-1

/ 1

N ^{= a} n ^R 0, n where R _q denotes the total resistance of the series combination of 13 resistors 10, 11, 12, ie.

N

-,

R '-> R, ⁰ Z_i ^ln ' to 0 where a _n is a dimensionless quantity from the interval (0,1), the operation of the whole circuit is simply described by the relation u ₂ = m / 2a _n - 1 / u _x = A _n u _x ;

where A _fi denotes amplification of the amplifier with the nth switch 14, 15 closed.

^R 10 ^e / 1 - and _L / R _q t ^R ln ^{/ and} n - ^and n ₊ l ^{Z R} o · ^R 1N ” ^and N ^R 0 ' dimensionless quantity M / m + 2 m X /.

For example, if it is desired that by connecting a switchable gain amplifier with the possibility of switching the gain polarity according to the invention, it is possible to realize a gain of 3, 2, 1, 0, -1,

-2, -3, will be m »3 and therefore» R / 3, Rj - R, R ₃ R / 2, R _1Q «0, R ^ -r R ₁₂ « ... = R ^ Rq / 6, ^R 17 ^e 0.

If, in a particular case, the wiring is provided with only two switches 14, 15 and if R ₁₀ · R ₁₂ ^e 0, Ryj · * is selected as an inverter, its operation will be described by the equation ^u 2 - ^ku l 'where k denotes the absolute transfer of the inverter. . The polarity of the output voltage will be determined by which of the switches 14, 15 is just closed.

Switchable gain amplifier wiring with the possibility of switching the gain polarity pc according to the invention can be applied, for example, in measuring exchanges and instruments with automatic or remote selection of the input or output range. It can also be applied as a precision inverter or a balanced modulator or demodulator

Claims (1)

Switchable gain amplifier with switchable gain polarity switching, equipped with input and output, comprising an operational amplifier with inverting and non-inverting input and output, at least two switches each having a control input, a control circuit with at least two outputs that are connected to their respective control inputs of each switch, input resistance, ground resistance, feedback resistance, a series combination of at least three resistors, and a common wire when an input resistor is connected between the input input and the inverting input of the opamp, between the inverting input of the operational amplifier and the output a feedback resistor is connected and an earthed resistor is connected between the inverting input of the operational amplifier and the common conductor, characterized in that a serial combination (13) is connected between the input (1) and the common conductor (3). at least three resistors (10, 11, 12), wherein between the resistors (10, 11, 12) of the series combination (13) are individually connected switches (14, 15) connected at their other end to a non-inverting input (6) of the operational amplifier / 4 /.