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AD6140 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD6140
Beschreibung Bandpass IF Subsystem
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
AD6140 Datasheet, Funktion
a
FEATURES
IF Subsystem
Bandpass ⌺⌬ Modulator
Variable-Gain Preamplifier with 13 dB of AGC Range
Mixer
AGC Detector
Op Amp for LNA Biasing
ECL-to-CMOS Level Translator
Ultralow Power Design
2.7 V Operating Voltage
4.8 mA Current Consumption
Power-Down Control
Small 20-Lead SSOP Package
APPLICATIONS
FLEX™, ReFLEX™ Receivers
Multimode Receivers
Bandpass ⌺⌬ IF Subsystem
AD6140
GENERAL DESCRIPTION
The AD6140 is a bandpass Σ∆ ADC IF IC for receivers requiring
a high dynamic range and multiple filter bandwidths. With an
external decimation filter, it creates a multibit analog-to-digital
converter. The AD6140 consists of a variable gain, low noise
preamplifier, mixer, AGC detector, bandpass Σ∆ modulator, an
ECL-to-CMOS level translator for the system clock, and an
auxiliary amplifier for use in biasing a discrete LNA. It is de-
signed to operate with Motorola’s ReFLEX chipset solution.
Contact Motorola directly for more information about the
ReFLEX chipset solution. With data and clock outputs at CMOS
logic levels, it interfaces to an external decimation filter. It comes in
a 20-lead plastic SSOP and operates over the –40°C to +85°C
industrial temperature range at 2.7 V.
IF_INPUT
LNA_SENSE
LNA_FORCE
AGC_CAPACITOR
0.1F
AGC_TC_SELECT
FUNCTIONAL BLOCK DIAGRAM
LO_IN+ LO_IN–
PREAMPLIFIER
MIXER POST
AMPLIFIER
LNA BIAS
AMPLIFIER
MIXER
AGC
DETECTOR
CIRCUIT
AD6140
MODULATOR
ECL-TO-CMOS
LEVEL-SHIFTER
BIAS SYSTEM
_DATA_OUT
_CLOCK_OUT
BUFFER_VDD
CLK_IN+
CLK_IN–
BUFFER_GND
VOLTAGE_REFERENCE_IN
RINT
AVDD AGND DGND DVDD POWER_DOWN
BIAS_RESISTOR
39k
FLEX and ReFLEX are trademarks of Motorola, Inc.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998






AD6140 Datasheet, Funktion
AD6140
5.2
TA = +25؇C
5.0
4.8
0
–50
4.6
4.4
2.5
2.6 2.7 2.8
POWER SUPPLY VOLTAGE – Volts
2.9
Figure 7. Supply Current vs. Power Supply Voltage
⌺⌬ MODULATION
A Σ∆ modulator uses feedback around a low noise quantizer
(1 bit in this case) in order to “shape” the spectrum of quantiza-
tion noise. Using this technique, we can shape noise away from
an arbitrary passband, within which we can place a modulated
signal. A Σ∆ modulator reproduces the input, but adds quanti-
zation noise, which can be digitally removed with a filter, known
as a decimation filter. Applying this technique to bandpass
signals results in an analog-to-digital converter suitable for
converting the IF signals in a digital radio.
The output of the AD6140’s Σ∆ modulator is shown in Figure
9. As can be seen, the noise is shaped away from a narrow band-
width, within which we place a signal (a sine wave in this case)
resulting in a narrowband, high dynamic range digital represen-
tation of the analog input.
–100
RESPONSE FROM 0kHz TO (fS /2)kHz
–150
0
500 1000 1500 2000 2500 3000 3500
FREQUENCY – kHz
Figure 9. Output Spectrum of AD6140
PRODUCT OVERVIEW
The AD6140 is a bandpass Σ∆ analog-to-digital converter IF
IC for dual conversion receivers requiring a high dynamic range
and multiple filter bandwidths. It consists of a variable gain, low
noise preamplifier, mixer, automatic gain control (AGC) detec-
tor, bandpass Σ∆ modulator, an ECL to CMOS level translator
and an auxiliary amplifier for use in biasing a discrete LNA.
The low noise preamplifier accepts a first IF input at 49.6 MHz
from 16.4 µV p-p to 63.2 mV p-p. It provides a variable gain
from 12 dB to 25 dB.
The mixer accepts an LO frequency of 49.792 MHz or
49.408 MHz, resulting in an IF frequency of 192 kHz. The LO
level should be 200 mV p-p differential. It is ac-coupled to the
AD6140. The mixer operates in the linear region, hence the
gain of the mixer is a function of the LO level. As a result, spe-
cial care must be taken to ensure that the LO level is 200 mV p-p,
IF_INPUT
LNA_SENSE
LNA_FORCE
AGC_CAPACITOR
0.1F
AGC_TC_SELECT
LO_IN+ LO_IN–
PREAMPLIFIER
MIXER POST
AMPLIFIER
LNA BIAS
AMPLIFIER
MIXER
AGC
DETECTOR
CIRCUIT
AD6140
MODULATOR
ECL-TO-CMOS
LEVEL-SHIFTER
BIAS SYSTEM
_DATA_OUT
_CLOCK_OUT
BUFFER_VDD
CLK_IN+
CLK_IN–
BUFFER_GND
VOLTAGE_REFERENCE_IN
RINT
AVDD AGND DGND DVDD POWER_DOWN
BIAS_RESISTOR
39k
Figure 8. Functional Block Diagram
–6– REV. 0

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