Document
U4080B
Voice-Switched Circuit for Handsfree Operation
Description
The voice switched speakerphone integrated circuit, U4080B, incorporates a variety of functions (see below). The versality of the device is further enhanced by the provision of a large number of pins giving access to internal circuit points.
Features
D Operates on telephone lines, integrated reference
voltage regulation
D Output power: 100 mW at a 25-Ω load with peak
limitation
D Linear volume control D Monitoring system for background sound level D Wide operating dynamic range through signal
compression
D Chip select pin for active/standby operation
Block Diagram / Application Circuit
Figure 1. Block diagram and application circuit
TELEFUNKEN Semiconductors Rev. A1, 20-May-96
1 (15)
Preliminary Information
U4080B
Pin Description
Pin 1 Symbol Function R1 Load resistance. Pin 14 Symbol Function GND1 High current ground pin for the speaker
2
RTG
3 4
TI TO
5
TLI
6
TLO
7
RLI
8
RLO
9
MIC
10
MICO
11
CP1
12
CP2
13
TDI
Provides reference current for the transmit and receive attenuators. Transmit attenuator nominal gain resistor. Transmit channel gain is inversely proportional to the resistance RTG connected to Pin 2. Transmit attenuator input. Input resistance is 5 kΩ Transmit attenuator output. Drives the input of the transmit level detector and the external circuit which drives the telephone line. Transmit level detector input. Sets the detector level. Sensitivity to transmit channel signals increases when the value of the resistor decreases. Transmit level detector output. The external RC-element sets the time the comparator will hold the system in the transmit mode after speech ceases. Receive level detector input. An external resistance connected to the pin sets the detection level. Sensitivity to receive channel signals increases when the resistor decreases. Receive level detector output. RC-element connected at the pin sets the time the comparator will hold the system in the receive mode after the receive signal expires. Microphone amplifier input. Input impedance is 10 kΩ and the bias voltage is approximately equal to VB. Microphone amplifier output. Gain is set internally at 34 dB (50 V/V). RC circuit for holding background noise level. The transmit detector compares the CP1 voltage with the speech signal from CP2. Capacitor for detecting the speech signal for comparison with the background noise held at Pin 11 (CP1). Transmit detector input. The microphone amplifier output is coupled to the TDI pin through an external resistor.
15
SAO
16 17
V+ AGC
18
CS
19 20
SAI VCC
21
VB
22 23
GND2 TDO
24
VCI
25
ACF
amplifier output stage. GND1 voltage should be within 10 mV of the ground voltage of Pin 22. Speaker amplifier output. It will source and sink up to 100 mA when ac coupled to the speaker. Gain is set internally at 34 dB (50 V/V). DC supply. A capacitor from this pin to VB stabilizes the speaker amplifier gain control loop, and additi.