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SA900

I/Q transmit modulator

Philips Electronics 

Philips Semiconductors

I/Q transmit modulator

Preliminary specification

SA900

AC ELECTRICAL CHARACTERISTICS (continued)

SYMBOL PARAMETER

TEST CONDITIONS

LIMITS

MIN

TYP

DUALTX

3rd order

-35

-42

(cont.) Linearity (0dB VGA, I and Q inphase)

5th order

-55

7th order

-65

Carrier suppression (I and Q quadrature)

VGA = 0dB

-35

-45

Carrier suppression (I and Q quadrature)

VGA = –40dB

-28

-33

Sideband suppression

I and Q quadrature

-35

-45

869 to 894MHz

–104

824 to 849MHz

–47

Spurious output

2 to 824MHz

–41

849 to 869MHz

–41

894MHz to 8.49GHz

–41

TXLO and harmonics

–21

Broadband noise (0dB VGA)

869 to 894MHz

935 to 960MHz

–136

–136

Adjacent channel noise power

@30kHz

–95

Alternate channel noise power

@60kHz

–101

Q/Q Baseband quadrature differential input

Max frequency

0.8

Differential modulation level

0.61

0.8

Differential input impedance

101

I/I

Baseband inphase differential input

Max frequency

0.8

Differential modulation level

0.61

0.8

Differential input impedance

10

Buffered TXLO differential outputs (AC

coupled)

Frequency range

900

VSWR (single-ended)

2:1

LO_1/2 Output impedance

single-ended

50

differential

100

Output level

single-ended, 50Ω

differential, 100Ω

50

90

100

180

NOTES:

1. Guaranteed by design.

2. Needs a different matching component. Max test frequency is 850MHz with test circuit shown in Figure 11.

MAX

21

1.01

21

1.01

1040

UNITS

dBc

dBc

dBc

dBc

dBc

dBc

dBm

dBc

dBc

dBc

dBc

dBc

dBm/Hz

dBm/Hz

dBc/Hz

dBc/Hz

MHz

VP-P

kΩ

MHz

VP-P

kΩ

MHz

Ω

Ω

mVP-P

mVP-P

FUNCTIONAL DESCRIPTION

Dual Mode Operation

The SA900 transmit modulator provides direct single sideband

quadrature modulation of the difference of the TXLO and VCO

frequencies, while providing quadrature LO signals for the I/Q

modulator. The quadrature LO signals are modulated with high

linearity by the baseband inphase (I) and quadrature (Q) signals.

The summed modulator output produces the lower sideband, while

rejecting the upper sideband. The I and Q inputs also provide DC

biasing for the modulator inputs. The summed output of the

modulator goes to a variable gain amplifier (VGA) to control the

output level, it has 40.0dB of attenuation control range, with 0.63dB

steps. The power control function is programmed by means of a

6-bit word (see Table 3). The VGA output drives the power amp

output stage to provide +2dBm average minimum power level (at

0dB power control) into 50Ω, in conjunction with external matching

components on DUALTX. The AD (AMPS/DUAL) and the SE

(synthesizer enable) bit control the power up/down of the DUAL

mode function. The transition of the TXEN, from low to high turns

on the modulator. The falling edge of the TXEN signal disables the

synthesizer and modulator. The TXLO is a system supplied LO

signal. The SA900 buffers the TXLO signal (LO_1/2) for use with

the system synthesizer (such as the SA7025) to form the system LO

synthesizer loop. The DUAL mode can also be used for AMPS

operation. The AMPS and DUAL mode modulation is generated by

the system DSP IC to provide the required I/Q baseband modulation

for the SA900. The DUAL output provides low broadband noise

output power (so that the receiver sensitivity is not degraded) and

high linearity to meet cellular phone system needs. Table 1 provides

the VGA power control limits.

The SA900 DUALTX output is externally matched with either a shunt

inductor to VCC and a series capacitor or a shunt inductor to VCC

and a series inductor. This matches the DUALTX output to 50Ω.

Values of the matching components are dependent on PCB layout,

typical values are shown in Figure 9.

1997 Sept 16

9

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