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ET-IL34118 Datasheet(PDF) 5 Page - Estek Electronics Co. Ltd |
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ET-IL34118 Datasheet(HTML) 5 Page - Estek Electronics Co. Ltd |
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5 / 12 page  ATTENUATOR CONTROL BLOCK The Attenuator Control Block has the seven inputs described above: - Tthe output of the comparator operated by RLO2 and TLO2 (microphone/speaker side) - designated C1. - The output of the comparator operated by RLO1 and TLO1 (Tip/Ring) side) - designated C2. - The output of the transmit background noise monitor - designated C3. - The output of the receive background noise monitor - designated C4. - The volume control. - The dial tone detector. - The AGC circuit. The single output of the Control Block controls the two attenuators. The effect of C1-C4 is as follows: Inputs Output C1 C2 C3 C4 Mode Tx Tx 1 X Transmit Tx Rx Y Y Fast Idle Rx Tx Y Y Fast Idle Rx Rx X 1 Receive Tx Tx 0 X Slow Idle Tx Rx 0 0 Slow Idle Rx Tx 0 0 Slow Idle Rx Rx X 0 Slow Idle X = Don’t Care; Y = C3 and C4 are not both 0 A definition of the above terms: 1) “Transmit” means the transmit attenuator is fully on (+6.0 dB), and the receive attenuator is at max. attenuation (-46 dB). 2) “Receive” means both attenuators are controlled by the volume control. At max. volume, the receive attenuator is fully on (6.0 dB), and the transmit attenuator is at max. attenuation (- 46 dB). 3) “Fast Idle” means both transmit and receive speech are present in approximately equal levels. The attenuators are quickly switched (30 ms) to idle until one speech level dominates the other. 4) “Slow Idle” means speech has ceassed in both transmit and receive path. The attenuators are then slowly switched (1 second) to the idle mode. 5) Switching to the full transmit or receive modes from any other mode is at the fast rate (30 ms). A summary of the truth table is as follows: 1) The circuit will switch to transmit if: a) both transmit level detectors sense higher signal levels relative to the respective receive level detectors (TLI1 versus RLI1, TLI2 versus RLI2), and b) the transmit background noise monitor indicates the presence of speech. 2) The circuit will switch to receive if: a) both receive level detectors sense higher signal levels relative to the respective transmit level detectors, and b) the receive background noise monitor indicates the presence of speech. 3) The circuit will switch to the fast idle mode if the level detectors disagree on the relative strengths of the signal levels, and at least one of the background noise monitors indicates speech. For example, refferring to the Expanded Logic Diagram (Figure 8), if there is sufficient signal at the microphone amp output (TLI2) to override the speaker signal (RLI2), and there is sufficient signal at the receive input (RLI1) to override the signal at the hybrid output (TLI1), and either or both background monitors indicate speech, then the circuit will be in the fast idle mode. Two conditions which can cause the fast idle mode to occur are a) when both talkers are attempting to gain control of the system by talking at the same time, and b) when one talker is in a very noisy environment, forcing the other talker to continually override that noise level. In general, the fast idle mode will occur infrequently. 4) The circuit will switch to the slow idle mode when a) both talkers are quiet (no speech present), or b) when one talker’s speech level is continuously overriden by noise at the other speaker’s location. The time required to switch the circuit between transmit, receive, fast idle and slow idle is determined in part by the components at the CT pin (Pin 14). A schematic of the CT circuitry is shown in Figure 4 and operates as follows: - RT is typically 120 kΩ, and CT typically 5.0 µF. - To switch to the receive mode, I1 is turned on (I2 is off), charging the external capacitor to +240 mV above VB. (An internal clamp prevents further charging of the capacitor.) - To switch to the transmit mode, I2 is turned on (I1 is off) bringing down the voltage on the capacitor to -240 mV with respect to VB. - To switch to idle quickly (fast idle), the current sources are turned off, and the internal 2.0 k Ω resistor is switched in, discharging the capacitor to VB with a time constant = 2.0 KΩ x CT. - To switch to idle slowly (slow idle), the current sources are turned off, the switch at the 2.0 k Ω resistor is open, and the capacitor discharges to VB through the external resistor RT with a time constant = RT x CT. BEIJING ESTEK ELECTRONICS CO.,LTD 5 ET- IL34118 |
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