Multi-channel amplifying device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Audio equipment

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Amplifying devices, the number of channels of which can reach several tens, are used in systems for collecting information from sensors in biomedical equipment, in thermal imaging scanning devices, and in many other areas of radio electronics [1–4].

I present to the readers' judgment a multi-channel amplifying device with electronic regulation of the voltage gain, which differs from those proposed in the popular literature [5. 6] by the fact that it uses semiconductor diodes as controlled elements [7]. These simplest semiconductor devices, as compared to more complex bipolar or field-effect transistors, usually used in adjustable units of amplifying devices [8, 9], as a rule, have a smaller technological spread of electrical parameters. The use of semiconductor diodes as controlled elements in the described multichannel amplifying device made it possible to achieve by simple means a relatively small spread in the gain of individual channels with gain control limits acceptable for many practical applications and a level of nonlinear distortion.

Main Specifications

• Number of amplification channels.........32
• The upper value of the voltage gain, not less than .......... 1000
• Limits of regulation of the voltage gain, dB, not less than .......... 15
• Spread of the voltage gain of individual channels relative to the average value, °о, not more than .......... 5
• Coefficient of non-linear distortion, °o, not more than .......... 5
• Operating frequency interval, Hz. not less than ..........20...150 000
• Control voltage, V..........0...5
• Supply voltage, V .......... 9
• Total power consumption W not more than .......... 1

Fig. 1

A schematic diagram of the amplifying device is shown in fig. 1 It consists of identical amplifying channels A1-A32 and a common for all channels control unit AZZ. Adjust the gain of the channels with the resistor R1 "Gain" Channels A1-A32 are identical in scheme, so only A1 is described below.

The channel consists of two stages of amplification at the op-amp 1DA1 1DA2 Capacitors 1C1, 1C2 and 1C4 determine the lower and upper limits of the channel bandwidth, respectively, the capacitor 1C3 is a filter in the power circuit. Resistors 1R5, 1R9 set the control current of operational amplifiers.

The gain of the first stage of the channel is determined by the ratio of the resistances of the resistors 1R1 and 1R4. Resistors 1R1 and 1R2 form a voltage divider, which increases the allowable value of the constant component at the input to 2,5R2 / (R1 + R2) V, preventing a possible reversal of the voltage polarity on the oxide capacitor 1C1. The resistor 1R2 has no practical effect on the gain.

The channel gain control, which is performed by the second stage on the op-amp 1DA2, is implemented by changing the conductivity of the diodes 1VD1, 1VD2 when the voltage supplied to the control input changes (pin 7 of the channel). With an increase in voltage at this input, the conductivity of the 1VD2 diode increases, due to which the resistance of the 1VD21R7 circuit decreases, and the current through the 1VD1 diode increases. As a result, the conductivity of the 1VD1 diode increases, and the resistance of the 1VD11R3 circuit decreases.

The 1VD1 diode and the 1R3 resistor are included in the negative feedback circuit covering the op-amp 1DA2, therefore, as the resistance of the 1VD11R3 circuit decreases, the stage gain increases. When the voltage at the control input decreases, the above processes occur in the opposite direction and the voltage gain decreases.

Fig. 2

On fig. 2 shows the dependence of the increment of the voltage gain DeltaK and relative to its minimum value, equal to 175 and taken as zero, on the control voltage UNnP, measured at the middle output of the resistor R1 "Gain" according to the circuit.

The AZZ control unit includes a bias voltage source necessary to ensure the normal operation of the op-amp channels in the unipolar power supply mode. The source consists of an op-amp 33DA1 and a transistor 33VT1. From the emitter of the buffer transistor 33VT2, voltage is removed to the control inputs of the channels. The nodes of the control unit AZZ and channels A1-A32 are powered by +5 V from the voltage regulator 33DA2. A variable resistor R1 "Gain" is connected to the same source.

in the amplifying device, oxide-semiconductor tantalum capacitors K53-56 and ceramic K10-17v are used. designed for surface mounting. All capacitors are soldered to the board from the print side. Resistors - S2-29V and S2-33, resistor R1 "Gain" - SP4-1a KT503B transistors can be replaced by any silicon npn transistors with similar parameters. Chips 1407UDZ and 140UD12 can be replaced by K1407UDZ and K140UD12. 140UD1201 K140UD1201 and A776N, respectively. Instead of KR142EN5A, stabilizer 7805 can be used.

Fig. 3

Channels A1-A32 and the AZZ control unit are mounted on printed circuit boards made of fiberglass laminated on one side with a thickness of 1 mm. A drawing of the printed circuit board of the channel is shown in fig. 3, and the control unit boards - in fig. four.

Fig. 4

The printed circuit boards of the channels and the control unit are placed in a common metal case, equipped with input and output connectors. To enable remote control, the resistor R1 "Gain" is located outside the housing.

The establishment of channels and the control unit of features does not have it performed according to known methods. If necessary, by selecting the resistor 33R2, a bilateral symmetrical limitation of the maximum output signal of channels A1-A32 is achieved. By selecting the capacitor NC4, the amplitude-frequency characteristic of the corresponding channel is corrected in the region of upper frequency values.

An estimate of the relative spread of the voltage gain coefficient xi of each channel is performed according to the formula

xi = (1 - Kg Kigs) 100%,

where K, - channel voltage gain; KL, p - arithmetic mean of the voltage gains of all channels. The relative spread of the channel gains is equalized in the control interval by a selection of resistors NR3, NR7 or diodes NVD1, NVD2.

Literature

1. Yarichin E. M., Shurygin N. A. Multi-channel amplifier - Devices and experimental technique 1986, No. 5. p. 123-125
2. Multichannel decoupling amplifier. - Electronics, 1975. No. 14, p. 83 84
3. Furman I., Zvonarev E. Logarithmic, programmable, integrating and voltage-controlled amplifiers from Texas Instruments Burn-Brown - Electronic components, 2005, p. 85-89.
4. Makarov A. S., Omelaev A. I., Filippov V. A. Introduction to the technique of developing and evaluating scanning thermal imaging systems - Kazan. Unipress, 1998, pp. 8-15.
5. Eritsev V., Tokarev V., Fedorov S. Electronic gain control. - Radio 1980. No. 2, p. 38
6. V'lnarov N. Predulsilvatel with electronically regulated on silvaneto. - Radio, television, electronics. 1981, no. 5, p. 28.
7. Sindinsky V. Remote gain control. - Radio, 1968. No. 3, p. 40, 41
8. Kisterny N. Electronic signal level regulator - Radio, 1989, No. 11, pp. 49-52.
9. Kreydich S. Field-effect transistor controllers - Radio, 1980, No. 2, p. 35-37.

Author: O. Ilyin, Kazan; Publication: radioradar.net

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