AD9276-65EBZ Analog Devices Inc, AD9276-65EBZ Datasheet - Page 26

• Manufacturer Part Number: AD9276-65EBZ
• Description: 65MSPS ADC Converter Evaluation Board
• Manufacturer: Analog Devices Inc

Specifications of AD9276-65EBZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: ADC
• Kit Application Type: Data Converter
• Silicon Core Number: AD9276
• Number Of Adc's: 1
• Number Of Bits: 12
• Sampling Rate (per Second): 65M
• Data Interface: Serial, SPI™
• Inputs Per Adc: 1 Differential
• Input Range: *
• Power (typ) @ Conditions: 195mW @ 40MSPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9276
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9276
I/Q Demodulator and Phase Shifter
The I/Q demodulators consist of double-balanced passive mixers.
The RF input signals are converted into currents by transconduc-
tance stages that have a maximum differential input signal
capability matching the LNA output full scale. These currents
are then presented to the mixers, which convert them to base-
band (RF − LO) and twice RF (RF + LO). The signals are phase
shifted according to the codes programmed into the SPI latch
(see Table 8). The phase shift function is an integral part of the
overall circuit. The phase shift listed in Column 1 of Table 8 is
defined as being between the baseband I or Q channel outputs.
As an example, for a common signal applied to a pair of RF inputs
to an AD9276, the baseband outputs are in phase for matching
phase codes. However, if the phase code for Channel 1 is 0000
and that of Channel 2 is 0001, then Channel 2 leads Channel 1
by 22.5°.
Table 8. Phase Select Code for Channel-to-Channel Phase Shift
Φ Shift
0°
22.5°
45°
67.5°
90°
112.5°
135°
157.5°
180°
202.5°
225°
247.5°
270°
292.5°
315°
337.5°
I/Q Demodulator Phase
(SPI Register 0x2D[3:0])
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Rev. 0 | Page 26 of 48
Dynamic Range and Noise
Figure 53 is an interconnection block diagram of all eight
channels of the AD9276. More channels are easily added to the
summation (up to 32 when using an
amplifier) by wire-OR connecting the outputs as shown. In
beamforming applications, the I and Q outputs of a number
of receiver channels are summed. The dynamic range of the
system increases by the factor 10 log
number of channels (assuming random uncorrelated noise).
The noise in the 8-channel example of Figure 53 is increased
by 9 dB, whereas the signal quadruples (18 dB), yielding an
aggregate SNR improvement of (18 − 9) = 9 dB.
The output-referred noise of the CW signal path depends on the
LNA gain, the selection of the external summing amplifier, and
the value of R
important to know the active low-pass filter (LPF) values, R
and C
channel are 2 kΩ for R
implement a 100 kHz single-pole LPF. In the case where eight
channels are summed, R
If the RF and LO are offset by 10 kHz, the demodulated signal is
10 kHz and is passed by the LPF. The single-channel mixing gain
from the RF input to the AD8021 output (for example, I1´, Q1´)
is approximately the LNA gain for R
0.8 nF.
This gain can be increased by increasing the filter resistor while
maintaining the corner frequency. The factor limiting the
magnitude of the gain is the output swing and drive capability
of the op amp selected for the I-to-V converter, in this example,
the AD8021. Because any amplifier has limited drive capability,
there is a finite number of channels that can be summed. The
channel-summing limit relates directly to the current drive
capability of the amplifier used to implement the active low-
pass filter and current-to-voltage converter. The maximum
sum, when the AD8021 is used, is 32 channels of the AD9276;
that is, four AD9276s (4 × 8 = 32 channels) can be summed in
one AD8021.
FILT
, shown in Figure 53. Typical filter values for a single
FILT
. To determine the output-referred noise, it is
FILT
FILT
and 0.8 nF for C
and C
FILT
FILT
10
AD8021
are 250 Ω and 6.4 nF.
(N), where N is the
and C
FILT
; these values
FILT
as the summation
of 2 kΩ and
FILT