CH1840D ET Cermetek Microelectronics, CH1840D ET Datasheet - Page 3

• Manufacturer Part Number: CH1840D ET
• Manufacturer: Cermetek Microelectronics

Specifications of CH1840D ET

• Operating Temperature Classification: Industrial
• Pin Count: 12
• Lead Free Status / RoHS Status: Supplier Unconfirmed

Cermetek Microelectronics, Inc.
Figure 3. Low Power Ring Detection
For live voice or DTMF, when the CH1840 family
products are in voice mode, the output can be 0 dBm.
Hence, by applying a 0dBm signal to the CH1840D
and a +9.5 dBm signal to the CH1840, it will achieve
the maximum signal output.
The D designation refers to differential input between
the XMIT (+) and (-) pins. This is required and is a
convenient input for certain types of modem ship sets.
RECEIVE SIGNAL
Receive Signal is presented at RCV with respect to
GND and must be AC coupled to your receive input.
The CH1840 does not add any gain to the receive
signal.
strength of 9dBm to below –50 dBm for data mode and
up to 0 dBm strength when DTMF and live voice are
being received.
EXCESSIVE SIGNAL DETECT
FCC Part 68 rules limit the average power of data
signals transmitted to the phone line. To meet this
requirement, the CH1840 monitors the transmit audio
signal at XMIT. If the signal level exceeds 0 dBm.
The output PSQ is normally LOW. It is set HIGH when
©2004 Cermetek Microelectronics, Inc.
CH1840 Family
CH1840
CH1840D
Receive signals can vary from a maximum
Normal Insertion Loss
-9.5 dB
0 dB
Page 3
excessive Power is detected and returns LOW when
the transmitted signal is unsquelched.
The squelch feature is defeated when Voice Mode is
selected on the Data/Voice pin.
always becomes inactive when the CH1840 is in Voice
Mode.
synthesized voice, the
signal must be treated as Data per FCC; thus Data
Mode must be selected on the Data/Voice pin.
2-WIRE TO 4-WIRE CONVERTER
This block has two functions: (1) it applies the XMIT
signal to the phone line, (2) it subtracts this signal from
the total signal on the phone to produce the received
signal.
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
XMIT signal applied to the signal returned is called
trans-hybrid rejection. The CH1840 has a high trans-
hybrid loss, which is at least 18dB rejection from 300
Hz to 4 KHz bandwidth.
VOICE SIGNALS
Voice signals are much more complex in nature than
data signals. A voice signal is comprised of numerous
frequencies combined at varying intensities. Whereas
a data signal is comprised of no more than a few
discreet frequencies.
voice signals receive more attention before connecting
to the telephone lines.
The FCC restricts voice and data signals to between
300 Hz and 3300Hz. This is because the Telephone
Company uses frequencies below 300 Hz for low-
speed tele type and frequencies above 3300 Hz for
internal signaling and multiplexing.
Data signals easily meet the FCC requirements
without additional filtering. However, bandpass filters
are essential for voice communication.
A bandpass filter is utilized on the transmit line. This
filter ensures that the signal meets FCC requirements.
It also shapes the signal to minimize the phone line
distortion.
The accuracy of this subtraction process
Note:
CH1840 Family of Low Profile DAA Modules
When
Document No. 607-0011 Revision C (09/09)
This difference dictates that
transmitting
The PSQ output
recorded
or