C
ermetek
microelectronics
CH1840
Low Profile Data Access Arrangement (DAA) Modules
INTRODUCTION
The CH1840 is an ultra small, low profile Data Access Arrange-
ment (DAA). Its modular construction and single +5 Volt D.C. power
requirement simplify your development process. Specifically de-
signed for both voice and data, this device allows direct connec-
tion of these circuits to the telephone lines. The CH1840 has FCC
Part 68 registration that can be transferred to your product. Simply
attach the included registration sticker to the outside of your prod-
uct. This eliminates the costs and delays associated with Part 68
testing and registration.
The CH1840 has also been designed to meet the requirements of
Canada’s Department of Communication (DOC). However, it is
necessary to register your product with the DOC before use in
Canada.
The CH1840 requires only 1.5 square inches of circuit board space
and presents a profile of only 0.35 inches in height. This DAA can
either be mounted directly on a printed circuit board or socketed.
Connection is made through 0.025 inch square pins on 0.10 inch
centers. The telephone line connection is made through a user
supplied RJ-11 jack.
The CH1840 DAA is designed for use with a variety of voice circuitry
and LSI modem/fax chip sets. This device is ideal for fax and
modem applications up through V.32bis. The CH1840 is pin com-
patible with the CH1817.
FEATURES
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Works with all modem chip sets
Available in 0 dB, -6 dB, and -9 dB insertion losses
Available in extended temperature operation,
-40
o
C to +85
o
C
Complete DAA function
Voice and data
FCC Part 68 registered
Registration conveyed to user
Hook switch control
Ring detection
Single +5V operation
Pulse dial capability
FUNCTIONAL DESCRIPTION
The operation of the CH1840 can be broken down into the
functional blocks shown in Figure 1.
1) Phone line control
2) Billing delay
3) Ring detection
4) Signal Path
5) 2- to 4-wire converter
Control inputs and status outputs for the CH1840 are compat-
ible with 5 Volt CMOS. See the Electrical Specifications.
Phone Line Control
In the Public Switched Telephone Network (PSTN), the wires
from a telephone to the phone company’s central office (CO) are
referred to as the local loop.
Figure 1. CH1840 Functional Block Diagram
© 2000 Cermetek Microelectronics, Inc.
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Document No. 607-0011 Rev. A (5/00)
Drawing current from the local loop signals the central office that
the telephone is Off Hook, that is, either answering a call or prepar-
ing to place a call. In the CH1840, this function is controlled by the
OFFHK signal. When this input is LOW, the CH1840 is On-Hook,
indicating to the central office it is not using the line. The CH1840
can pulse dial by toggling the OFFHK input.
For data calls, FCC Part 68 rules require silence on the phone line
for at least 2 seconds after the call has been completed to allow
central office to exchange billing information. The CH1840 as-
sures conformance to this requirement by starting a two-second
timer on the LOW to HIGH transition to OFFHK and squelching
transmitted signals until the time expires. The CH1840 defeats
this function when Voice Mode is selected on the Data/Voice pin.
Ring Detection
The central office signals an incoming call by placing a ring signal
on the local loop. The CH1840 monitors the loop for this signal.
The Ring Indication output, RI, is normally HIGH. When ringing
appears, RI is set LOW during the typically 2 second ring period
and is restored to HIGH for the typically 4 seconds between rings.
The ring detection circuit is designed to prevent false indications
due to noise or pulse dialing on the line.
The RI output of the CH1840 is diode protected so that an external
pull-up resistor (R> 100Kohm) to +5V may be utilized to activate
the ring detection circuit when the DAA is not connected to power.
This can be handy with designs in which power consumption is of
concern. When circuited in this manner, there is virtually no current
draw until a ring signal is present. See Figure 3.
Figure 3. Low Power Ring Detection
The CH1840 attenuates the transmit signal by 9.5 dB, 0 dB for the
D option). Thus, a transmit signal of 0 dBm for the CH1840 ( -9.5
dBm for D) applied to XMIT will comply with the FCC Part 68 re-
quirement for data signals of -9dBm across Tip and Ring. In all
cases in the data mode, the CH1840 prevents the signal level
from being greater than -9 dBm at Tip and Ring.
For live voice or DTMF, when the CH1840 family products are in
voice mode, the output can be 0 dBm. In voice mode, the squelch
will not let the output signal exceed 0 dBm. Hence, by applying a
0 dBm signal to the CH1840D and a +9.5 dBm signal to the
CH1840, it will achieve the maximum signal output.
CH1840 Family
CH1840
CH1840D
Nominal Insertion Loss
-9.5 dB
0 dB
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 CH1840D, a
XMIT(+) and XMIT(-) pin designation provides a differential input.
Figure 2. Typical Application
© 2000 Cermetek Microelectronics, Inc.
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Document No. 607-0011 Rev. A (5/00)
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.
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 sub-
traction 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 ap-
plied to the signal returned is called trans-hybrid rejection. The
CH1840 has a high trans-hybrid loss, which is at least 18 dB re-
jection from 300 Hz to 4 KHz bandwidth.
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 re-
ceived.
Excessive Signal Detect
FCC Part 68 rules limit the average power of data signals trans-
mitted to the phone line. To meet this requirement, the CH1840
monitors the transmit audio signal at XMIT. If the signal level ex-
ceeds 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.
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 frequen-
cies below 300 Hz for low-speed teletype 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 com-
munication.
A bandpass filter is utilized on the transmit line. This filter ensures
that the signal meets FCC requirements. It also shapes the sig-
nal to minimize the phone line distortion.
Table 1. Pin Descriptions
© 2000 Cermetek Microelectronics, Inc.
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Document No. 607-0011 Rev. A (5/00)
SAMPLE APPLICATION
Figure 2 illustrates a typical application of the CH1840. When
transmitting data the controller must assert the D/V pin low to
provide the two second billing delay required by the FCC. When
transmitting voice signals, the controller should drive the D/V pin
high. This disables the billing delay, and power squelch.
One of the requirements of an FCC approved DAA is that the
signal transmitted to Tip and Ring does not exceed -9.0 dBm.
The CH1840 incorporates an automatic squelch. If the signal
exceeds -9.5 dBm, the DAA will discontinue transmission until the
signal returns to acceptable levels. The PSQ output indicates
when the squelch circuit has been activated. By utilizing PSQ to
drive the illustrated LED circuit, a visual indication of the squelch
activation can be attained.
DESIGN CONSIDERATIONS
The following guidelines for your product desgin must be fol-
lowed to meet the requirements of FCC Part 68 rules.
1) The mounting of the DAA in the final assembly must be
made so that it is isolated from exposure to any hazard-
ous voltages within the assembly. Adequate separation
and restraint of cables and cords must be provided.
2) The circuitry from the registered unit to the telephone line
must be provided in wiring that carries no other circuitry
than that specifically allowed in the rules ( such as A and
A1 leads).
3) See Section “For Your User’s Manual” for information that
must appear in your User’s Manual.
4) Connection to the phone line should be made through a
standard RJ-11C jack or equivalent.
5) Circuit board traces from the CH1840’s TIP and RING
pins must exceed 0.1 inch spacing to one another and
0.2 inches spacing from all other traces or other conduct-
ing material. Traces should have a nominal width of 0.020
inches or greater.
6)
TIP and RING traces should be as short as possible and
should be oriented to prevent direct or induced coupling with other
signals on the host circuit card.
7)
No additional application circuitry should be connected be-
tween the CH1840 and the phone line RJ-11C jack, except as
described in note 10 below.
8) The registration label included with the product must be affixed
to the outside of your product where it is easily visible to your end
user.
9) The CH1840 Module is a sensitive subsystem that should be
treated as any other integrated component. Pay special attention
to the power supply to the DAA. The device handles signals in the
millivolt range. Although it is designed to handle noise in the
power supply, steps should be taken to assure the noise level
does not exceed 50 mV peak-to-peak. Failure to provide such
operating conditions could cause the CH1840 to malfunction.
10) The CH1840 DAA meets or exceeds the hazardous voltage,
surge and leakage requirements of the FCC. For applications that
connect to Canadian phone lines, governed by the DOC (Depart-
ment of Communications) and to further protect the CH1840 from
field failure due to poor lines, a higher level of transient protection
is required, thereby making mandatory the circuit consisting of two
fuses and one varistor as shown in Figure 4. Adding these three
devices will not affect FCC or U.L. registration.
Components L1, L2, C1, C2 are optional and serve two
purposes. First, they restrict high frequency signals from
reaching the phone line and thereby add EMI protection.
Second, they protect against externally generated RFI
from degrading the modem’s ability to operate on proper
carrier signals. Adding these devices will not affect
FCC, DOC, or U.L. registration.
Figure 4. Telephone Line Interfaces
© 2000 Cermetek Microelectronics, Inc.
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Document No. 607-0011 Rev. A (5/00)
Mounting the CH1840
The CH1840 can be soldered directly to the host circuit card or
installed in sockets. Direct soldering provides the most sound
connection. To avoid the problems of flux contamination, hand
soldering is preferred to wave soldering. Many socket manufac-
turers offer socket strips that accept the 0.025 inch square pins
on 0.10 inch centers. When using mechanical sockets, restraint
of the CH1840 should be provided to keep it seated during ship-
ment. Plastic cablewraps are secure yet easily removed.
6. Special FCC rules apply to equipment connected behind a
PBX or KTS.
7. Changes in Attestation Procedure for Plugs and Jacks: (Name
of applicant) attests that the network interface plugs or jacks
used on this equipment comply with and will continue to com-
ply with the mechanical requirements specified in Part 68, Sub-
part F, specifically the dimensions, tolerances and metallic plat-
ing requirements. The compliance of these connectors will be
assured by purchase specifications and incoming inspection.
Documentation of such specifications and/or inspections will
be provided by the FCC within 30 days of their request for the
same.
FOR YOUR USER’S MANUAL
The Part 68 rules require the following or the equivalent informa-
tion be provided to the end user of equipment containing a DAA:
FCC NOTICE TO THE USERS
1. UPON REQUEST ONLY, you must provide the following data to
your telephone utility company (telco):
a) Notice of intention to install or permanently remove an FCC
Part 68 registered device or system, and the *FCC Registra-
tion Number.
b) *The Ringer Equivalence Number (REN) (see device label).
Note that if several devices are connected to the same line,
the RENs must not add up to more than 5.0 (A or B). This
REN figure is important to your telco.
c) *The (USOC) jack type to be provided by the telco. Typically
this will be RJ-11C/W for single lines.
*The *-flagged items above are noted on the equipment’s
FCC Compliance label.
2.
This device may not be used on telco-operated coin phone
lines. Party lines and privately owned coin-phones are
subject to local State regulatory policies, and possible
additional State special requirements.
3. The telco has the right to make changes to its network which
may affect the operation of your equipment, provided you are
given adequate advance written notice to permit correct oper-
ation.
4. In case of operational problems, disconnect your unit by
removing the modular plug from the telco jack. If your regular
phone (or other device or system) still works properly, your
[product name] has a problem and must remain disconnected
and (officially) serviced or returned for repairs. If upon the
above connection, your regular service still has problems,
notify your telco that they may have a problem. Request
prompt service at no cost to you the user. If a problem is
found in premises wiring not telco-installed, you are subject
to a service charge. If a fault is in telco-installed wiring, you
may be subject to a service call charge.
5.
Unless otherwise noted in the User’s Manual (e.g.: fuses,
etc.), user may not under any circumstances (in or out of war-
ranty) attempt any service, adjustments or repairs on this
unit. It must be returned to the factory or authorized U.S.
service agency for all such work. Locations (or phone
numbers) of factory or authorized U.S. service points are listed
in this user’s manual.
© 2000 Cermetek Microelectronics, Inc.
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Document No. 607-0011 Rev. A (5/00)
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