ch1840 ETC-unknow, ch1840 Datasheet - Page 3

• Manufacturer Part Number: ch1840
• Description: Profile Data Access Arrangement Modules
• Manufacturer: ETC-unknow

© 2000 Cermetek Microelectronics, Inc.
The D designation refers to differential input between the XMIT
(+) and XMIT (-) pins. This is required and is a convenient input
for certain types of modem chip 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. Receive signals can vary from
a maximum strength of –9 dBm 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, prior to the DAA attenuation, the transmit
audio is prevented from reaching the phone line until the average
input level is again below 0 dBm. The output PSQ is normally
LOW. It is set HIGH when excessive power is detected and
returns LOW when the transmitted signal is unsquelched.
Since FCC part 68 rules have no limitation to the signal strength
of live voice transmission, the squelch feature is defeated when
Voice mode is selected on the Data/Voice pin. The PSQ output
always becomes inactive when the CH1840 is in Voice Mode.
Note: When transmitting recorded or synthesized voice, the signal
must be treated as Data per FCC; thus Data Mode must be
selected on the Data/Voice pin.
PIN
10
11
12
1
2
3
4
5
6
7
8
9
XMIT(+)
OFFHK
XMIT(-)
NAME
RING
PSQ
GND
RCV
VCC
N/C
D/V
TIP
RI
I/O
I/O
I/O
O
O
O
-
I
I
I
I
I
I
TIP. Direct connection to the telephone line through a standard jack.
RING. Direct connection to the telephone line through a standard jack.
Not Used. Please leave unconnected.
OFF HOOK, Input. When set Low, the CH1840 is placed on-Hook. When set HICH, the CH1840 is placed Off-Hook to
answer or place a call. This input can also be used for pulse dialing. NOTE: When answering incoming calls in response to
a ring indication on RI, internal relay contact degradation may occur if OFFHK is set HICH before RI returns to its HIGH
state.
RING INDICATION, Output. RI is driven low during the typically 2-second ring period and HIGH during the typically 4
seconds between rings. RI is otherwise HICH. NOTE: RI pulses square wave along with ring signal frequency. The square
wave can be suppressed to produce an envelope of the AC ring with the application circuit shown in Figure 2.
DATA/VOICE SELECT, Input. When driven LOW or left unconnected, Data mode is selected and the Billing Delay and
Power Squelch are enabled. When driven HIGH, voice mode is selected and the Billing Delay and Power Squelch are
disabled.
POWER SQUELCH, Output. PSQ indicates the status of the signal limiting squelch circuit. When PSQ is HIGH, the
transmit path is squelched. PSQ is also active when On-Hook and in Data Mode.
RECEIVE, Output. RCV is the audio signal received from the phone line. This output symmetrical with respect to +2.5C.
AC coupling is recommended for most designs.
Input must be used with pin 11 in differential mode only. When not used, please leave unconnected.
+5V power Supply, Input.
TRANSMIT, Input. Analog signal input. Audio data and voice signals presented here will be monitored for excessive
power, filtered through a bandpass, and applied to the phone line unless squelched. One input pin of two when used in
differential mode with pin 9.
SIGNAL and POWER COMMON GROUND, Input.
Table 1. Pin Description
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. The accuracy of this
subtraction process 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 18-dB
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. This difference dictates that voice
signals receive more attention before connecting to the telephone
lines.
The FCC restricts voice and data signals to between 300 Hz and
3300 Hz. This is because the telephone company uses frequencies
below 300 Hz for low speed teletype and frequencies above
3300Hz 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.
Page 3
FUNCTION
Document No. 607-0011 Rev. A (5/00)