AD6630AR Analog Devices Inc, AD6630AR Datasheet - Page 5

• Manufacturer Part Number: AD6630AR
• Description: IC IF GAIN BLOCK W/CLAMP 16-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD6630AR

• Rohs Status: RoHS non-compliant
• Current - Supply: 30mA ~ 48mA
• Frequency: 250MHz
• Gain: 22dB ~ 24dB @ 250MHz
• Noise Figure: 4dB
• P1db: 7.5dBm
• Package / Case: 16-SOIC (0.300", 7.50mm Width)
• Test Frequency: 250MHz
• Voltage - Supply: 8.5V ~ 10.5V
• Rf Type: -

REV. 0
THEORY OF OPERATION
The AD6630 amplifier consists of two stages of gain. The first
stage is differential. This differential amplifier provides good
common-mode rejection to common-mode signals passed by
the SAW filter. The second stage consists of matched current
feedback amplifiers on each side of the differential pair. These
amplifiers provide additional gain as well as output drive capa-
bility. Gain set resistors for these stages are internal to the de-
vice and cannot be changed, allowing fixed compensation for
optimum performance.
Clamping levels for the device are normally set by tying CLLO
or CLHI pins to the negative supply. This internally sets bias
points that generate symmetric clamping levels. Clamping is
achieved primarily in the output amplifiers. Additional input
stage clamping is provided for additional protection. Clamping
levels may be adjusted to lower levels as discussed below.
APPLICATIONS
The AD6630 provides several useful features to meet the needs
of radio designers. The gain and low noise figure of the device
make it perfect for providing interstage gain between differential
SAW filters and/or analog-to-digital converters (ADC). Addi-
tionally, the on-board clamping circuitry provides protection for
sensitive SAW filters or ADCs. The fast recovery of the clamp
circuit permits demodulation of constant envelope modulated
IF signals by preserving the phase response during clamping.
The following topics provide recommendations for using the
AD6630 in narrowband, single carrier applications.
Adjusting Output Clamp Levels
Normally, the output clamp level is set by tying either CLLO or
CLHI to ground or V
8.5 dBm and 12 dBm levels by selecting the appropriate exter-
nal resistor.
To set to a different level, CLLO and CLHI should be tied
together and then through a resistor to ground. The value of the
resistor can be selected using the following equation.
R
14 4
EE
. –
. It is possible to set the limit between
OUTPUT
0 0014
.
OSCILLATOR
ANTENNA
–104dBm
–43dBm
–28dBm
–16dBm
–15dBm
–1dB
CLAMP
LOCAL
15dB –9dB
(
dBm
AD6630 INPUT
)
–91dBm
–30dBm
–15dBm
–3dBm
–2dBm
Figure 6. GSM Design Example
–2dB
15dB
–5dB
AD6630 OUTPUT
SAW
–5–
–67dBm
–6dBm
+9dBm
+9dBm
+9dBm
AD6630
24dB
This equation is derived from measured data at 170 MHz. Clamp
levels vary with frequency, see Figure 5. Output clamp levels
less than 8.5 dBm will result in damage to the clamp circuitry
unless the absolute maximum input power is derated. Similarly,
the output clamp level cannot be set higher than 12 dBm.
Matching SAW Filters
The AD6630 is designed to easily match to SAW filters. SAW
filters are largely capacitive in nature. Normally a conjugate
match to the load is desired for maximum power transfer.
Another way to treat the problem is to make the SAW filter look
purely resistive. If the SAW filter load looks resistive there is no
lead or lag in the current vs. voltage. This may not preserve
maximum power transfer, but maximum voltage swing will
exist. All that is required to make the SAW filter input or output
look real is a single inductor shunted across the input. When the
correct value is used, the impedance of the SAW filter becomes
real.
EVALUATION BOARD
Figures 9, 10 and 12 refer to the schematic and layout of the
AD6630AR as used on Analog Devices’ GSM Diversity Re-
ceiver Reference Design (only the IF section is shown). Figure
14 references the schematic of the stand-alone AD6630 evalua-
tion board and uses a similar layout. The evaluation board uses
center tapped transformers to convert the input to a differential
signal and AD6630 outputs to a single connector to simplify
evaluation. C8, C9 and L2 are optional reactive components to
tune the load for a particular IF frequency if desired.
–5dB
SAW
AD6600 INPUT
Figure 8. Saw Filter Model (170 MHz)
DIVERSITY
MAIN
+4dBm
+4dBm
+4dBm
–71dBm
–10dBm
AD6600
Figure 7. Clamp Level Resistor
400
V
EE
AD6620
3pF
R
GENERATOR
DSP
CLAMP
47nH
9.7
15.2pF
AD6630