DS_1903_032
73M1903 Data Sheet
5.2 Transmit Power - dBm
To calculate the analog output power, the peak voltage must be calculated and the peak to rms ratio
(crest factor) must be known. The following formula can be used to calculate the output power, in dBm
referenced to 600 Ω.
Pout (dBm) = 10 * log [ ( Vout (V) / cf )2 / ( 0.001 * 600 ) ]
The following example demonstrates the calculation of the analog output power given a 1.2 kHz FSK tone
(sine wave) with a peak code word value of 11,878 sent out by the DSP.
The differential output voltage at TXAP-TXAN will be:
With FreqFctr = 1.02, (See Figure 10)
Vout (V) = 2 * (11,878/32,767) * 0.6640625 * 0.8889 * 1.36 * 1.0 * 1.4454 * 1.02 = 0.841 Vpk.
The output signal power will be:
Pout (dBm) = 10 * log [(0.841 / 1.41)2 / (0.001 * 600) ] = - 2.29 dBm.
Table 13: Peak to RMS Ratios for Various Modulation Types
Transmit Type Crest Factor Max Line Level
V.90
QAM
DPSK
4.0
-12 dBm
-9 dBm
-9 dBm
2.31
1.81
FSK
1.41
1.99
-9 dBm
DTMF
-5.7 dBm
5.3 Control Register (CTRL1): Address 00h
Reset State 08h
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ENFE
Unused
TXBST1 TXBST0 TXDIS
RXG1
RXG0
RXGAIN
ENFE
1 = Enable the digital filters and analog front end.
0 = Disable the analog blocks shut off the clocks to the digital and analog receive/transmit
circuits.
TXBST1
1 = Add a gain of 1.335 dB (16.6%) to the transmitter; also the common mode voltage of the
transmit path is increased to 1.375 V. This is intended for enhancing DTMF transmit
power only and should not be used in data mode.
0 = No gain is added
TXBST0
1 = A gain of 1.65 dB (21%) is added to the transmitter
0 = The gain of the transmitter is nominal
TXDIS
1 = Tri-state the TXAP and TXAN pins, provides a bias of VBG into 80 kΩ for each output pin
These bits control the receive gain as shown in Table 12.
RXG1:0
RXGAIN
1 = Increase the gain of the receiver by 20 dB.
Rev. 2.0
23
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
