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參數(shù)資料
| 型號： | MAX990 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Micropower.Low-Voltage.UCSP/SC70.Rail-to-Rail I/O Comparators |
| 中文描述： | 微功耗、低電壓、UCSP/SC70封裝、滿擺幅輸入/輸出比較器 |
| 文件頁數(shù)： | 3/8頁 |
| 文件大?。?/td> | 315K |
| 代理商： | MAX990 |
E
MAX9981 Evaluation Kit
_______________________________________________________________________________________
3
Detailed Description
The MAX9981 is a highly integrated downconverter. RF
and LO baluns are integrated on-chip, as well as an LO
buffer and a SPDT LO input select switch. The EV kit cir-
cuit consists mostly of supply decoupling capacitors and
DC-blocking capacitors, allowing for a simple design-in.
Supply Decoupling Capacitors
Ceramic capacitors C5, C6, C9, and C10 are 100pF
used for high-frequency bypass on the supply. C13
and C17 are 220pF bypass capacitors for IF frequen-
cies. C16 and C20 are used to provide IF ground for
the center tap of T1 and T2. Although called out,
replacing C16 and C20 with a short circuit causes little
to no change in performance.
DC-Blocking Capacitors
The MAX9981 has internal baluns on the RFMAIN,
RFDIV, LO1, and LO2 inputs. These inputs have almost
0
resistance at DC. C1 and C4 are 33pF DC-blocking
capacitors on the RF ports and C7 and C8 are 15pF DC
blocks for the LO ports. C14, C15, C18, and C19 are
used to block DC current from flowing into the trans-
formers along with providing flexibility for matching.
RFBIAS
Bias current for the mixer is set with resistors R1 and
R2 (267
±1%). This value was carefully chosen for
best linearity and lowest supply current through testing
at the factory. Changing this value, or using lower toler-
ance resistors degrades performance.
IF±
The MAX9981 employs a differential IF output to offer
increased IP2 system performance. The IF outputs look
like an open collector with 1.8pF of differential capaci-
tance. Inductors L1
–
L4 are used to resonate out the on-
chip and evaluation board capacitance at the IF
frequency of interest along with providing a low-resis-
tance path for biasing of the IF amplifier. R3
–
R6 pro-
vide a real impedance used to establish the 200
differential impedance. C14, C15, C18, and C19 pro-
vide DC blocking along with adding in the flexibility for
tuning. The 4:1 baluns (T1 and T2) transform the 200
differential impedance to 50
single ended for ease of
measurement. The EV kit IF is matched for operation
over the 70MHz to 100MHz frequency range.
Resistors R3
–
R6 affect the gain of the mixer. For a typi-
cal 2.0dB gain, 137
resistors are used for R3
–
R6.
Higher mixer gain can be realized by increasing R3
–
R6
and retuning L1
–
L4, C14, C15, C18, and C19 for IF
impedance matching. For example, R3 through R6 =
250
, L1 through L4 = 330nH, C14 = C15 = C18 = C19
= 56pF yields a mixer gain of 4.6dB at 70MHz IF with
an IF return loss of 12dB.
As the differential IF outputs are relatively high imped-
ance (200
), they are more susceptible to component
parasitics. It is often good practice to relieve the
ground plane directly underneath large components to
reduce associated shunt-C parasitics.
LOSEL
The EV kit includes a 47k
pullup resistor to allow for
easy selection of the LO port. Providing a ground at
TP3 selects LO2, while leaving TP3 open selects LO1.
To drive TP3 from an external source, follow the limits
called out in the MAX9981 data sheet. Logic voltages
should not be applied to TP3 without the +5V applied.
Doing so can cause the on-chip ESD diodes to conduct
and could damage the part.
Modifying the EV Kit
The RF and LO inputs are broadband matched, so
there is no need to modify the circuit for use anywhere
in the 825MHz to 915MHz RF range (725MHz to
1085MHz LO range).
Retuning for a different IF is as simple as scaling the
values of the IF pullup inductors up or down with fre-
quency. The IF outputs look like an open collector with
3.6pF to ground (1.8pF differential) from the chip. This
capacitance, along with approximately 5.6pF from the
evaluation board, can be resonated out at the frequen-
cy of interest by proper selection of the bias inductor
(L1
–
L4). To determine the inductor value use the follow-
ing equation:
The IF output network is tuned for operation at approxi-
mately 70MHz, so a 560nH inductor is used. For lower
IF frequencies (i.e., larger component values), maintain
the component
’
s Q value at the cost of a larger case
size unless it is unavoidable.
f
L x C
IF
=
1
2
π
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX990EKA | 制造商:Maxim Integrated Products 功能描述:- Cut Tape Product 制造商:Rochester Electronics LLC 功能描述: |
| MAX990EKA+ | 制造商:Maxim Integrated Products 功能描述:COMPARATOR 2 R-R I/O 2.75V/5.5V 8PIN SOT-23 - Rail/Tube |
| MAX990EKA+T | 功能描述:校驗(yàn)器 IC Dual uPower Comparator RoHS:否 制造商:STMicroelectronics 產(chǎn)品: 比較器類型: 通道數(shù)量: 輸出類型:Push-Pull 電源電壓-最大:5.5 V 電源電壓-最小:1.1 V 補(bǔ)償電壓（最大值）:6 mV 電源電流（最大值）:1350 nA 響應(yīng)時(shí)間: 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SC-70-5 封裝:Reel |
| MAX990EKA-T | 功能描述:校驗(yàn)器 IC RoHS:否 制造商:STMicroelectronics 產(chǎn)品: 比較器類型: 通道數(shù)量: 輸出類型:Push-Pull 電源電壓-最大:5.5 V 電源電壓-最小:1.1 V 補(bǔ)償電壓（最大值）:6 mV 電源電流（最大值）:1350 nA 響應(yīng)時(shí)間: 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SC-70-5 封裝:Reel |
| MAX990ESA | 功能描述:校驗(yàn)器 IC RoHS:否 制造商:STMicroelectronics 產(chǎn)品: 比較器類型: 通道數(shù)量: 輸出類型:Push-Pull 電源電壓-最大:5.5 V 電源電壓-最小:1.1 V 補(bǔ)償電壓（最大值）:6 mV 電源電流（最大值）:1350 nA 響應(yīng)時(shí)間: 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SC-70-5 封裝:Reel |
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