In triode, the gate-to-source voltage is high enough to allow current flow from drain to source, and the nature of the induced channel is such that the magnitude of the drain current is influenced by the gate-to-source voltage and the drain-to-source voltage. As the drain-to-source voltage increases, the triode region transitions to the saturation region, in which drain current is ideally independent of drain-to-source voltage and thus influenced only by the physical characteristics of the FET and the gate-to-source voltage. The saturation-region relationship between gate-to-source voltage V GS and drain current I D is expressed as follows:. Further increases continue to affect the channel because the pinch-off point moves closer to the source:.
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All rights reserved. The UTC TEAA is a bipolar integrated circuit that performs all speech and line interface functions required in fully electronic telephone sets. It performs electronic switching between speech and dialling.
The IC operates at a line voltage down to 1. PAD No. Vref is temperature compensated and can be adjusted by means of an external resistor RVA. Vref equals 3. The voltage at pin SLPE is proportional to the line current. Changing RSLPE will affect more than the DC characteristics; it also influences the microphone and DTMF gains, the gain control characteristics, the sidetone level and the maximum output swing on the line. It may also be used to supply peripheral circuits such as dialling or control circuits.
RCCint is the internal equivalent resistance of the voltage supply, and Irec is the current consumed by the output stage of the earpiece amplifier. The DC line current flowing into the set is determined by the exchange supply voltage Vexch , the feeding bridge resistance Rexch , the DC resistance of the telephone line Rline and the reference voltage Vref. With line currents below 7.
This means that more sets can operate in parallel with DC line voltages excluding the polarity guard down to an absolute minimum voltage of 1. At currents below 7. This is called the low voltage area. The equivalent impedance of the circuit is illustrated in Fig. Automatic gain control is provided on this amplifier for line loss compensation. The CGAR capacitor provides a first-order low-pass filter.
The output voltage of the receiving amplifier is specified for continuous wave drive. The maximum output swing depends on the DC line voltage, the RCC resistor, the ICC current consumption of the circuit, the IP current consumption of the peripheral circuits and the load impedance.
The automatic gain control varies the gain of the microphone amplifier and the gain of the receiving amplifier in accordance with the DC line current. The control range is 5. This resistor enables the Istart and Istop line currents to be increased the ratio between Istart and Istop is not affected by the resistor. Mute function pin MUTE The mute function performs the switching between the speech mode and the dialling mode. A pull-up resistor is included at the input.
These tones can be heard in the earpiece at a low level confidence tone. The automatic gain control has no effect on the DTMF amplifier.
In practice, Zline varies considerably with the line type and the line length. Therefore, the value of Zbal should be for an average line length which gives satisfactory sidetone suppression with short and long lines.
The suppression also depends on the accuracy of the match between Zbaland the impedance of the average line. The anti-sidetone network for the UTC TEAA as shown in Application information circuit attenuates the receiving signal from the line by 32 dB before it enters the receiving amplifier. The attenuation is almost constant over the whole audio frequency range. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury.
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