MC34016 Просмотр технического описания (PDF) - Motorola => Freescale

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MC34016

Cordless Universal Telephone Interface

Motorola => Freescale 

MC34016

With the component values of the typical application, the

inductor has a value of about 2.4 H and RDC1 equals 470 kΩ.

In the audio range of 300–3400 Hz, these components form

a fairly large parallel impedance to RSET and CSET.

Therefore, the set impedance is mainly determined by the

passive network RSET and CSET. In the typical application,

RSET is 600 Ω, but it can easily be replaced by a complex

network to obtain a complex set impedance.

Active Set Impedance

An active set impedance can be obtained by placing a

resistor between pin LAI and SRF (RSRF) as shown in

Figure 11. By doing so, the MC34016 itself generates the ac

set impedance and RSET and CSET can be omitted. An

equivalent network now equals:

RDC1

RSRF

CM

RDC1 x CM x RS

((RDC1 + RSRF) x RS/RSRF) – RS

RS

Ignoring the effect of the inductor and the parallel path

RDC1 + RSRF again for audio frequencies, the set

impedance is now determined by:

+ ) ZSET

RS

RSRF

x

(RDC1

RSRF)

With RS = 50 Ω and RDC1 = 470 kΩ, RSRF should be 43 kΩ

to obtain a 600 Ω set impedance. To obtain a complex set

impedance, RDC1 can be made complex. In such case, the

dc mask can be adjusted with the dc value of RDC1 and the

set impedance can be adjusted with the ac value of RDC1. An

application with an active set impedance is interesting,

particularly in countries like France, where with the dc current

regulation mask, rather high line voltages can be reached.

With a passive set impedance, this would result in a high cost

for capacitor CSET.

TRANSMIT CHANNEL

Inputs

The inputs Tx1 and Tx2 are designed to handle large signal

levels of up to +3.0 dBm. The input impedance for both Tx1

and Tx2 equals 30 kΩ. The inputs are designed for

symmetrical as well as asymmetrical use. In asymmetrical

drive, one input can be tied to Gnd via an external capacitor.

Gain

The gain from inputs Tx1 and Tx2 to the line is dependent

on the set impedance, the line load impedance and dc slope

resistor RS in the following way:

+ ) ATX

1

6 x RS

x

ZSET

ZSET

x

Zline

Zline

With ZSET = 600 Ω, Zline = 600 Ω and RS = 50 Ω the gain

equals 0 dB. By setting Bit 4 of Register 2 to 1, the gain is

raised by 6.0 dB.

MOTOROLA ANALOG IC DEVICE DATA

Outputs

In order to transmit signals to the line, the output stage of

the MC34016 (line driver) modulates the zener previously

described. To guarantee stability of the output stage

capacitor CSTB of 100 pF is required

SIDETONE

The MC34016 is equipped with a double Wheatstone

bridge architecture to optimize sidetone. One sidetone

network is used for short lines and one for long lines.

Switchover between both networks is dependent on line

current and is described in the automatic gain control section.

Different sidetone equations apply depending on whether a

passive or an active set impedance is set.

Sidetone Cancellation with Passive Set Impedance

In a passive set impedance application, the set impedance

is a part of the equations for optimum sidetone. For short

lines optimum cancellation occurs if:

+ ) ZHS1

RHS2

RS

x

ZSET

ZSET

x

Zlineshort

Zlineshort

with: Zlineshort = impedance of a short telephone line

and for long lines:

+ ) ZHL1

RHL2

RS

x

ZSET

ZSET

x

Zlinelong

Zlinelong

with: Zlinelong= impedance of a long telephone line

Sidetone Cancellation with Active Set Impedance

In the active set impedance application, the set impedance

does not appear in the equations for optimum sidetone

cancellation as it does in the passive application. For short

lines, optimum cancellation occurs if:

+ ZHS1

RHS2

RS

x

Zlineshort

and for long lines:

+ ZHL1

RHL2

RS

x

Zlinelong

RECEIVE CHANNEL

Inputs

The inputs HYS and HYL have an input resistance of 30 kΩ

and can handle signals up to 800 mVpp. This corresponds to a

signal at the telephone line of about 8.0 dBm in the typical

application. The switchover from HYS to HYL is dependent on

line current and described in the automatic gain control

section.

Gain

The overall gain from the line to the outputs Rx1 and Rx2

for short lines and passive impedance equals:

+ ) ARX

7.6

x

R14′

R14′ ZHYS

For active impedance it follows:

+ ) ǒ ) Ǔ ARX

7.6

x

R14′

R14′ ZHYS

x

1

R1 x ZHYS

R14 x ZSET

In these relations, R14′ is the resistor R14 in parallel with

the input impedance at HYS of 30 kΩ. The gain for long

lines can be derived by replacing ZHYS and R14 by ZHYL

7

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