Philips Semiconductors

Preliminary specification

SA900

I/Q transmit modulator

1997 Sept 16

9

SYMBOL

PARAMETER

TEST CONDITIONS

LIMITS

UNITS

SYMBOL

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

DUALTX

3rd order

-35

-42

dBc

(cont.)

Linearity (0dB VGA, I and Q inphase)

5th order

-55

dBc

7th order

-65

dBc

Carrier suppression (I and Q quadrature)

VGA = 0dB

-35

-45

dBc

Carrier suppression (I and Q quadrature)

VGA = –40dB

-28

-33

dBc

Sideband suppression

I and Q quadrature

-35

-45

dBc

869 to 894MHz

–104

dBm

824 to 849MHz

–47

dBc

Spurious output

2 to 824MHz

–41

dBc

849 to 869MHz

–41

dBc

894MHz to 8.49GHz

–41

dBc

TXLO and harmonics

–21

dBc

Broadband noise (0dB VGA)

869 to 894MHz

–136

dBm/Hz

Broadband noise (0dB VGA)

935 to 960MHz

–136

dBm/Hz

Adjacent channel noise power

@30kHz

–95

dBc/Hz

Alternate channel noise power

@60kHz

–101

dBc/Hz

Max frequency

0.8

MHz

Q/Q

Baseband quadrature differential input

Differential modulation level

0.8

Differential input impedance

k

Ω

Max frequency

0.8

MHz

I/I

Baseband inphase differential input

Differential modulation level

0.8

Differential input impedance

10

k

Ω

Buffered TXLO differential outputs (AC

coupled)

Frequency range

900

1040

MHz

VSWR (single-ended)

2:1

LO_1/2

Output impedance

single-ended

50

Ω

_

Output impedance

differential

100

Ω

Output level

single-ended, 50

Ω

50

90

Out ut level

differential, 100

Ω

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.

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 50

Ω, 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

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

Ω.

Values of the matching components are dependent on PCB layout,

typical values are shown in Figure 9.