ESL signal converter amplifier. Scheme, description

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ESL signal converter amplifier. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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The device offered to the attention of readers is designed to amplify and convert ESL signals. Before the design was set the task of independent regulation of the range and the constant component of the output signal, and with the possibility of obtaining both positive and negative pulses even at the maximum range.

Both regulators in the amplifier are not under the RF signal voltage, so they can be separated by some distance from each other, convenient for the user. Together with the ESL signal generator, the power amplifier was used to establish and study digital and analog devices.

Main Specifications

ECL input signal logic levels, V high .......-0,8
low .......-1,6
Input impedance, kOhm not less .......0,6
Output impedance, Ohm.......50
Output voltage swing, V, not less, at a load with a resistance of 50 Ohm ....... 2,5
Rise and fall time of output pulses, ns, no more .......10
Deviation from the horizontal top of the impulses,%, not more .......5

Rice. 1 (click to enlarge)

The amplifier circuit is shown in the figure. The input stage of the amplifier is differential, assembled on transistors VT1 and VT2 with a current generator on the transistor VT4. Diodes VD2 and VD3 set the reference voltage (-1,2 V). The difference between the ESL logic levels and the reference voltage is at least 200 mV, which is sufficient for complete switching of the differential stage [1].

The emitter follower on the transistor VT3 performs the function of an adjustable differential stage power supply. The upper (positive) level of the output voltage depends on the voltage set by the resistor R3.

When the voltage at the base of the transistor VT4 changes, the current of the differential stage changes. The output voltage swing depends on this current, and the upper (positive) level, set by the voltage on the basis of the VT3 transistor, practically does not change, and the lower (negative) level depends on the current of the VT4 transistor. The generated rectangular pulses are fed to an emitter follower made on a transistor VT5 with a current source VT7 in the emitter circuit.

Transistor VT6, together with resistors R15 and R16, form an analogue of a zener diode, designed to shift the level of the constant component, which is necessary to obtain a multi-polar output voltage.

The voltage drop across the LED HL1 is used as a reference for the current source on the transistor VT7.

The output stage is built on transistors VT8 - as an emitter follower and VT9 - as a current source for it. The current is approximately 80 mA. Inductor L1 increases the output impedance of the current source at high frequency by increasing the impedance of the emitter circuit. Zener diode VD5 reduces the power dissipated by the transistor VT8. Resistor R22 determines the output impedance of the amplifier and matches it with the load.

Resistors in the base circuits of transistors VT1, VT3, VT4, VT5, VT8, VT9 prevent the occurrence of parasitic self-excitation of the amplifier.

The input logic levels of the amplifier can be changed by appropriate selection of the reference voltage based on the transistor VT2, but you should make sure that there is no saturation of the differential stage transistors.

I did not design the printed circuit board of the amplifier. I assembled it on racks made of MLT-0,25 resistors with a conductive layer and leads removed, soldered to a plate of foil fiberglass.

When choosing transistors, it must be remembered that, with the exception of VT3, VT6, VT7, they must all have a cutoff frequency of the base current transfer coefficient of at least 900 MHz. Permissible power dissipation of the transistor VT7 - not less than 200 mW; to facilitate the thermal regime, a heat sink should be put on its body in the form of a spiral of copper or brass wire with a diameter of 0,5 ... 1 mm, coiled into a ring [2].

Chokes L1 - DM-0,6, L2 and L3 - DPM-1,2.

The stabilization voltage of the zener diode analogue on the transistor VT6 should be approximately 5 V, it is set by selecting the resistor R15. Instead of the transistor VT6, you can use the stabilizer KR142EN19 (TL431) - the control output is connected as the base of the transistor, the cathode - as a collector, the anode - as an emitter. In this case, the resistor R16 should be selected, not R15. The optimum should correspond to the ratio R15-R16.

Output transistors VT8 and VT9 should be installed on heat sinks with a usable area of at least 50 cm2.

To adjust the amplifier, the sliders of variable resistors R2 and R3 are set to the upper position according to the scheme and rectangular pulses with ESL levels with a frequency of 1 ... 2 kHz are fed to the input. A selection of resistor R15 achieves the absence of a constant component at the output. Make sure that transistors VT1 and VT2 do not enter saturation in the lower position of the R3 engine according to the scheme (the voltage on the collector of transistors should always be greater than the base voltage).

Loading the amplifier with a 50 ohm resistor and increasing the frequency to about 100 kHz, using an oscilloscope, they check the shape of the output pulses (the steepness of the front and fall of the pulses, the amplitude of the spikes, the horizontality of the top).

Literature

Naiderov V. Z., Golovanov A. I., Yusupov Z. F., Getman V. P., Galperin E. I. Functional devices on microcircuits. - M.: Radio and communication, 3, p. 3-1985.
Plotnikov V. Radiator for low-power semiconductor devices. - Radio, 1973, No. 7, p.27.

Author: E. Mammadov

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