CH1817LM 查看數據表（PDF） - Unspecified

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CH1817LM

Family of Low Profile DAA Modules

Unspecified 

Cermetek Microelectronics, Inc.

Hook Switch. The OFFHK input is used to control the

on-hook and off-hook status of the CH1817. When

OFFHK is low, the CH1817 is in the On-Hook State.

This indicates to the CO that the CH1817 is ready to

receive calls. When OFFHK is high, the CH1817

allows the CO supplied loop current to flow, indicating

either it is answering a call or preparing to place a call.

OFFHK

Input: Active High

Active Current: 4mA

CH1817 Family of Low Profile DAA Modules

TRANSMIT SIGNAL

The outgoing analog signal to be transmitted through

the phone line should be applied to the XMIT pin (with

respect to GND) and must be AC coupled as shown in

Figure 2. For the CH1817-D a XMIT (+) and XMIT (-)

pins provide a differential input. The CH1817-L

attenuates the transmit signal by 9.5dB, 0dB for the –D

option. Therefore, a transmit signal of 0dBm for the –L

option (-9.5 dB for –D) applied to XMIT will comply

with the FCC Part 68 requirement for data signals of –

9dBm across TIP and RING.

2-Wire To 4-Wire Hybrid Converter. This block has

two functions:

1. It applies the XMIT signal to the phone line.

2. It subtracts the desired signal from the total

outgoing signal on the phone line to derive the

RCV signal.

The accuracy of this derivation depends on how

closely the impedance of the phone line matches 600

Ohms. Generally, a small amount of the XMIT signal

will appear at RCV. The ratio of the applied XMIT

signal to the received XMIT signal is called Trans-

Hybrid Rejection, or Trans-Hybrid Loss. On a 600Ω

phone line, the CH1817 DAAs have very high trans-

hybrid rejection, typically 23 dB.

NOTE

The FCC requires that the DTMF tone not exceed

0dBm.

RECEIVE SIGNAL

The incoming analog signal appearing between TIP

and RING is presented at RCV with respect to GND

and must be AC coupled to the user equipment

receive input. The CH1817 does not gain the receive

signal. Receive signals can vary from a maximum

strength of –9dBm to below –50dBm.

RCV

Gain: 0dB

Out impedance: 100Ω

Typical Output Signal:

-9dBm to –50dBm

2.5Vrms to 0.27mVrms

Signal referenced to GND

AC coupling required

Attenuation

Input Impedance

CH1817-D

0dBm

150KΩ

XMIT

CH1817-L

9.5dBm

150KΩ

CH1817-DM

6.5dBm

150KΩ

CH1817-LM

6.5dBm

150KΩ

Figure 2. Typical CH1817 Application.

2002 Cermetek Microelectronics, Inc.

Page 2

Document No. 607-0007 Revision B (01/02)

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