SU1677846A1 - Ac amplifying device - Google Patents

Abstract

The invention relates to electronic technology and can be used as a low frequency amplifier in radio devices or as an AC amplifier in precision amplifiers with modulation and demodulation of the signal. The purpose of the invention is to increase the gain. The alternating current amplifier contains a differential amplifier 1, a voltage follower 2, a coupling capacitor 3, resistive dividers 4, 5, and a repeater 2 on an operational amplifier 6 and a resistor 7. The device provides high noise immunity due to the presence of a differential input, has a low bias voltage that provides a large operating range of output signals. This eliminates the need for large capacitors in the negative feedback circuit, and does not require the use of resistive voltage dividers with a large ratio of resistors. 1 il. 4ff yo

Description

The invention relates to electronic equipment and can be used in low-frequency amplifiers in radio devices or in AC amplifiers in precision amplifiers with modulation and demodulation of the signal.

The purpose of the invention is to increase the gain. .

The drawing shows a structural electrical diagram of an amplifying device for alternating current.

The AC amplifying device contains a differential amplifier (DU) 1, a voltage follower 2, an isolation capacitor 3, first and second resistive voltage dividers 4, 5, while the voltage follower 2 is made on an operational amplifier (OA) 6, a resistor 7.

Amplifier AC operates as follows.

The constant voltage applied to the inputs ВХ1, ВХ2 of the device, as well as the bias voltage of the remote control 1 are transmitted to the remote control output! but do not pass through the isolation capacitor 3 and therefore are absent at the output of the OUT device. In this case, the gain of the remote control 1. determined by the division coefficient of the first and second resistive dividers 4 and 5, can be close to unity. Therefore, the bias voltage is not amplified, which provides a low bias voltage at the output of the remote control 1. At the output (IN), the device also has a small bias voltage of the voltage follower 2, equal to the bias of the OU6.

If an alternating signal is supplied to the inputs of device ВХ1, ВХ2, then its in-phase component is not transmitted to ДУ 1, and the differential (difference) component from ДУ1 output passes through isolation capacitor 3 to the input of voltage follower 2, and goes to the output of the device OUT and to the second output of the first resistive divider 4, The signal coming to this pin is repeated in the remote control! superimposing on a signal equal to the amplified value of the differential component of the input variable signal, which leads to a significant amplification of the alternating signal even with a unity gain of the remote control!

The cutoff frequency is determined by the capacitance of the isolation capacitor 3 and the input resistance of the voltage follower 2 (resistor 7).

The stability of the device is ensured if the positive feedback in it is weaker than the negative in the entire operating frequency range, for which the transmission coefficient of the voltage follower 2 should be less than unity with a sufficiently high accuracy of the selection of resistors of the first and second resistive voltage dividers 4 and 5.

If the output voltage of the remote control 1 ivevy DU1 = (UbX1 - UBX2) KdU1 + Tsvyh.

where Ubxi., Ubx2 - voltage at VX inputs! BX2 device;

Tsvykh ~ voltage on the DEVICE;

Kdu1 - remote control gain! then the gain of the device K = Ivykh _______ Kdu) · Kpn 'UBX1 - UBX2 <1 \, .1 where Kpn is the transfer coefficient of the voltage follower 2;

R7 is its input resistance equal to the resistance of the resistor 7;

Sz is the capacitance of the isolation capacitor 3, ω is the circular frequency of the input signal; j- = A.

For a sufficiently high input frequency, the device gain

Kus =

KdU1 · Kpn - Kpn that with Kpn - * 1 will be significant even with Kdu1 =! The upper cutoff frequency is determined by the decrease in the frequency characteristics of the remote control 1 and voltage follower 2.

The set of features inherent in the proposed amplification device,. provides him with advantages over analogues. The device is characterized by high noise immunity due to the presence of a differential input, has a low bias voltage, which ensures a • wide working range of output signals. This eliminates the need for large capacitors in the 45 negative feedback circuit and does not require the use of resistive voltage dividers with a large ratio of resistors.

Thus, a large gain 5θ in the proposed device is achieved at low capacitance ratings and approximately equal resistances of the voltage divider resistors. This makes it possible to implement such a device in 55 hybrid-film or in a fully integrated version.

Claims (1)

Claim An AC amplifying device comprising a differential amplifier 5 st I, a starter whose output is connected through an isolation capacitor to the input of a voltage follower, the first and second resistive voltage dividers, the taps of which are connected respectively to the non-inverting and inverting inputs of the differential amplifier, while the first and second conclusions of the first resistive voltage divider are respectively the first input and output of an AC amplifying device. characterized in that, in order to increase the gain, the output of the voltage follower is connected to the second output of the first resistive voltage divider5, the output of the differential amplifier is connected to the first output of the second resistive voltage divider, the second output of which is the second input of the AC amplifier.