Datasheet

MAX19707
10-Bit, 45Msps, Ultra-Low-Power
Analog Front-End
30 ______________________________________________________________________________________
Using Op-Amp Coupling
Drive the MAX19707 Rx ADC with op amps when a
balun transformer is not available. Figures 10 and 11
show the Rx ADC being driven by op amps for AC-cou-
pled single-ended and DC-coupled differential applica-
tions. Amplifiers such as the MAX4454 and MAX4354
provide high speed, high bandwidth, low noise, and
low distortion to maintain the input signal integrity. The
op-amp circuit shown in Figure 11 can also be used to
interface with the Tx DAC differential analog outputs to
provide gain or buffering. The Tx DAC differential ana-
log outputs cannot be used in single-ended mode
because of the internally generated common-mode
level. Also, the Tx DAC analog outputs are designed to
drive a differential input stage with input impedance
≥ 70kΩ. If single-ended outputs are desired, use an
amplifier to provide differential-to-single-ended conver-
sion and select an amplifier with proper input common-
mode voltage range.
TDD Mode
The MAX19707 is optimized to operate in TDD applica-
tions. When FAST mode is selected, the MAX19707 can
switch between Tx and Rx modes through the T/R pin
in typically 0.5µs. The Rx ADC and Tx DAC operate
independently. The Rx ADC and Tx DAC digital bus are
shared forming a single 10-bit parallel bus. Using the 3-
wire serial interface or external T/R pin, select between
Rx mode to enable the Rx ADC or Tx mode to enable
the Tx DAC. When operating in Rx mode, the Tx DAC
bus is not enabled and in Tx mode the Rx ADC bus is
tri-stated, eliminating any unwanted spurious emissions
and preventing bus contention. In TDD mode, the
MAX19707 uses 84.6mW power at f
CLK
= 45MHz.
TDD Application
Figure 12 illustrates a typical TDD application circuit.
The MAX19707 interfaces directly with the radio front-
ends to provide a complete “RF-to-Bits” solution for
TDD applications such as 802.11, 802.16, DSRC, and
proprietary radio systems. The MAX19707 provides
several system benefits to digital baseband developers.
• Fast Time-to-Market
• High-Performance, Low-Power Analog Functions
• Low Risk, Proven Analog Front-End Solution
• No Mixed-Signal Test Times
• No NRE Charges
• No IP Royalty Charges
• Enables Digital Baseband to Scale with 65nm to
90nm CMOS
Figure 9. Balun Transformer-Coupled Differential-to-Single-
Ended Output Drive for Tx DAC
MAX19707
IDP
IDN
V
OUT
QDP
QDN
V
OUT
Figure 10. Single-Ended Drive for Rx ADC
MAX19707
0.1
μ
F
1k
Ω
1k
Ω
100
Ω
100
Ω
C
IN
22pF
C
IN
22pF
QAP
QAN
COM
IAP
IAN
0.1
μ
F
R
ISO
50
Ω
R
ISO
50
Ω
REFP
REFN
V
IN
0.1
μ
F
1k
Ω
1k
Ω
100
Ω
100
Ω
C
IN
22pF
C
IN
22pF
0.1
μ
F
R
ISO
50
Ω
R
ISO
50
Ω
REFP
REFN
V
IN