Altera^® Megafunction: Gain Generation

The NComm Gain Generation (GainGen) Megafunction is a Mitel ST-Bus compatible device providing from 1 to 32 user programmable gain levels used in telephony applications. The GainGen Megafunction can generate any decibel level of gain, both positive and negative, to a voice channel. The GainGen Megafunction also supports Mu-law to/from A-law encoding, and other parameters on a tone by tone basis, providing complete control over the tones being generated; the selected gain level for the given timeslot is controlled via software.

The GainGen MegaWizard^™ Plug-In (GainGen Plug-In) is used to specify and maintain the gain levels to be generated by the GainGen Megafunction. The GainGen Plug-In allows a user to configure new gain settings, edit existing new gain settings, and request Mu-law to/from A-law conversion. The GainGen Plug-In is fully integrated with the Altera MegaWizard™, providing a very simple yet powerful way to add new gain settings generation to a telephony or other application.

Target Applications · Network Switches · Digital Loop Carriers · Digital PBXs · International Voice Gateways · Telecom Altera® Family FLEX 10K

Main Features · Generates any decibel level of gain, positive and negative, used in telephony applications · Provides up to 32 user programmable gain levels · Supports both Mu-Law and A-Law encoding algorithms · Provides fully configurable gain control · MegaWizard^™Plug-In features gain setting, editing, and Mu-law to A-law and/or A-law to Mu-law conversion

Functional Description

The GainGen Megafunction requires only a TDM clock and a 125μs frame pulse as inputs and generates an ST-Bus compatible serial output stream and output frame pulse. A 32 channel ST-Bus stream example is shown below, the gains synthesized by the GainGen Megafunction are placed into the first time slots of the stream.

For the example shown to the right, gains have been defined with the GainGen Megafunction Plug-In. The GainGen hardware will synthesize the gains and place them into the 32 time slots of a ST-bus stream.

Customization : GainGen MegaWizard^™ Plug-In

The GainGen Megafunction is fully customizable with respect to the gain levels generated. With the associated GainGen MegaWizard^™ Plug-In, a user can create virtually any gain levels required by the target application. Additionally, the MegaWizard^™ Plug-In allows a user to minimize the amount of embedded array blocks (EABs) required to synthesize the gains, by calculating the least number of pulse code modulation (PCM) samples required to generate the desired levels.

Applications

· The GainGen Megafunction can be used to manage signal gains for a Small Office/Home Office PBX systems, Network Switches, Digital Loop Carriers, International Voice Gateways, and a host of other telecom situations.

SOHO PBX System:

Generally, telecom lines are engineered to manage a –6 db loss. Standard point-to-point connection loss would be managed as shown:

When the telecom line passes through a PBX, improper gain levels will lead to users having to strain to listen to some external calls and muffle the volume of calls within the internal phone network. In a well-balanced network, the correct gain levels are achieved regardless of where the points originate and terminate. In the application below, with GainGen software, 3 decibel losses are added to internal calls; three-party calls would require 2 db losses per line to achieve a total loss of 6 decibels . External calls require zero loss to each line as the –6 db loss in achieved in the external network. Further, with GainGen software, the PBX can better manage digital phone interfaces such as T1 connections & digital modems and analog interfaces such as a standard voice connections, analog modems & fax machines.

References

Mitel Semiconductor Corporation, ST-Bus Specification

Bellcore, FR-64, LATA Switching System Generic Requirements (LSSGR)

Bellcore, SR-TSV-002275, BOC Notes on the LEC Networks, Issue 2, April 1994

TIA, TR-41, User Premises Telecommunications Equipment Requirements

ITU, G.711, Pulse code modulation (PCM) of voice frequencies

Device Utilization Example

Device Utilization Examples
Gain	Device	Speed Grade	Utilization		Performance
			Logic Cells	EABs (1)	(2)
Mu-Law 8 TDM highways 4 Gain Levels 128 Timeslots/highway	10K20	-3	390	5	27.24Mhz
A-law 1 TDM highway 8 Gain Levels 32 Timeslots/highway	1K30	-1	95	5	60.24Mhz
Mu-Law A-Law (Law Conversion) 4 TDM highways 4 Gain Levels 32 Timeslots/highway	1K50	-1	226	9	53.19Mhz
Mu-Law A-Law (Law Conversion) 12 TDM highways 8 Gain Levels 128 Timeslots/highway	10K200	-1	582	19	35.58Mhz

Note:

1. EABs = Embedded array blocks
2. Frequency Requirements are dictated by the number of timeslots on the TDM highways. For all examples, the device performance exceeds the requirements for the TDM clocks.