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19-2092; Rev 0; 7/01
Upstream CATV Amplifier with On-Chip Anti-Alias Filter
General Description
The MAX3507 is a variable-gain power amplifier for use in CATV upstream transmitters. The variable-gain feature has 55dB of dynamic range and is controlled by a 3-wire SPITM bus. The device is capable of generating +64dBmV output (16QAM/QPSK) when driven with a +34dBmV nominal input signal. The on-chip anti-alias lowpass filter with 75MHz cutoff frequency saves system design cost and space. The optional positive slope generator provides system design flexibility. The device operates from a single +5V supply and draws 220mA nominal during transmit at max gain (100% duty cycle). For burst-type transmissions, the device is shut off between bursts to minimize noise and save power while still maintaining a match at the output. The device is optimized for high linearity with harmonic levels below -55dBc. The MAX3507 is available in a 28-pin QFN package and operates over the extended industrial temperature range (-40C to +85C). o 5MHz to 65MHz Operation o 55dB Gain Control Range o Optional Positive Slope Generator o 55dB Spurious-Free Dynamic Range Over Transmit Band
Features
o Built-In 5th-Order Elliptic Anti-Aliasing Filter
MAX3507
Ordering Information
PART MAX3507EGI TEMP. RANGE -40C to +85C PIN-PACKAGE 28 QFN
Applications
Cable Modem Upstream Transmitter Set-Top Box Upstream Transmitter Telephony Over Cable
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
VCC VCC
GND
GND
N.C.
VCC
EQ+
28 BIASF 1
EQ-
27
26
25
24
23
VCC 22 TXEN
21 BIAS CIRCUIT
DC+
VCC 20 N.C.
2
DC-
3 OPTIONAL EQUALIZER
GND VCC VCC
5-POLE ELLIPTIC FILTER
19
OUT+
4
18
OUT4:1 IMPEDANCE RATIO
5 SERIAL DATA
17 GAIN CONTROL 16
N.C.
IN+
6
CEXT
IN-
7 8 GND 9 CS 10 SDA 11 SCLK
MAX3507
12 GND 13 N.C. 14 SHDN
15
N.C.
VCC
DIGITAL CONTROL LINES
SPI is a trademark of Motorola, Inc. ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
ABSOLUTE MAXIMUM RATINGS
VCC, OUT+, OUT- to GND.....................................-0.5V to +8.0V Input Voltage Levels (all inputs), CEXT to GND ...........................................-0.3V to (VCC + 0.3V) Continuous Input Voltage (IN+, IN-) ..................................2Vp-p Continuous Current (OUT+, OUT-) ..................................120mA Continuous Power Dissipation (TA = +70C) 28-Pin QFN (derate 20.8mW/C above +70C) ..............1.67W Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +125C Bump Reflow Temperature ..............................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(MAX3507 EV Kit, VCC = +4.75V to +5.25V, VGND = 0, VTXEN = V SHDN = VCC, D7 = 1, TA = -40C to +85C, unless otherwise specified. No input signal applied. A 4:1 (300 to 75) impedance ratio balun is connected to differential output ports and balun output is terminated into a 75 load. Typical parameters are at VCC = +5.0V, TA = +25C.) (Note 1)
PARAMETER Supply Voltage D7 = 1, gain code = 127 (max gain) Supply Current Transmit Mode D7 = 1, gain code = 119 (gain of 28dB) D7 = 1, gain code = 64 (gain of 0dB) D7 = 0, gain code = 94 (gain of 0dB) Supply Current Transmit Disable Mode Shutdown Supply Current LOGIC INPUTS Input HIGH Voltage Threshold Input LOW Voltage Threshold Input HIGH Current Input LOW Current -100 2.0 0.8 100 V V A A VTXEN = VEE, V SHDN = VCC VTXEN = X, V SHDN = VEE CONDITIONS MIN 4.75 218 164 82 74 45 1 59 mA A TYP MAX 5.25 280 mA UNITS V
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter
AC ELECTRICAL CHARACTERISTICS
(MAX3507 EV Kit, VCC = +4.75V to +5.25V, VGND = 0, VTXEN = V SHDN = VCC, VIN = +34dBmV differential, TA = -40C to +85C, unless otherwise specified. A 4:1 impedance ratio (300 to 75) balun is connected to differential output ports and balun output is terminated into a 75 load. Typical parameters are at VCC = +5.0V, TA = +25C.) (Note 1)
PARAMETER CONDITIONS D7 = 1, gain code = 125 D7 = 1, gain code = 119 D7 = 1, gain code = 104 fIN = 5MHz, TA = 0C to +85C (Note 2) D7 = 1, gain code = 84 D7 = 1, gain code = 64 D7 = 0, gain code = 74 D7 = 0, gain code = 54 D7 = 0, gain code = 42 fIN = 65MHz, D7 = 1, gain code = 127 TA = 0C to +85C (Note 3) VOUT = 61dBmV, fIN = 42MHz, equalizer disabled (Note 3) VOUT = 61dBmV, fIN = 65MHz, equalizer disabled (Note 3) fIN = 5MHz to 65MHz, AV = -26dB to +30dB Gain Step Size fIN = 5MHz to 65MHz, AV = -26dB to +30dB, any 2-bit transition of D0, D1 fIN = 5MHz to 42MHz, D7 = 0, gain code = 109; D7 = 1, gain code = 81, TA = 0C to +85C Transmit-Disable Mode Noise Isolation in Transmit Disable Mode Transmit Mode Noise Transmit Enable Transient Duration Transmit Disable Transient Duration Transmit Disable/Transmit Enable Transient Step Size Input Impedance Output Return Loss Output Return Loss in Transmit Disable Mode Any BW = 160kHz from 5MHz to 65MHz, TXEN = VEE (Note 3) TXEN = VEE, fIN = 5MHz to 65MHz Any BW = 160kHz from 5MHz to 65MHz, gain = -26dB to +30dB (Note 3) TXEN input rise/fall time < 0.1s, TA = +25C (Notes 3, 4) TXEN input rise/fall time < 0.1s, TA = +25C (Notes 3, 4) D7 = 1, gain code = 119 (AV = >27dB), TA = +25C D7 = 0, gain code = 94 (AV = 0), TA = +25C (Note 3) fIN = 5MHz to 65MHz, single ended (Note 3) fIN = 5MHz to 42MHz in 75 system, D7 = 1, gain code = 125 (AV = 30dB) (Note 5) fIN = 5MHz to 42MHz in 75 system, TXEN = VEE (Note 5) 0.8 10 10 1.5 70 -54.5 2 2 100 5.2 0.7 0.6 MIN 29.6 26.8 19.5 9.7 -0.7 -10.5 -20.4 -27.2 29.0 -1.1 -2.1 -0.5 -0.7 0.5 1.0 1.0 1.3 1.4 -64 dBmV dB dBc s s mVp-p k dB dB dB +0.2 +0.3 TYP 31.1 28.3 20.9 10.9 0.5 -9.3 -19.1 -25.7 MAX 32.6 29.8 22.3 12.1 1.7 -8.1 -17.8 -24.2 dB UNITS
MAX3507
Voltage Gain (AV)
Gain Flatness
dB
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX3507 EV Kit, VCC = +4.75V to +5.25V, VGND = 0, VTXEN = V SHDN = VCC, VIN = +34dBmV differential, TA = -40C to +85C, unless otherwise specified. A 4:1 impedance ratio (300 to 75) balun is connected to differential output ports and balun output is terminated into a 75 load. Typical parameters are at VCC = +5.0V, TA = +25C.) (Note 1)
PARAMETER CONDITIONS Input tones at 42MHz and 42.2MHz, both at +31dBmV, VOUT = +58dBmV/tone Input tones at 65MHz and 65.2MHz, both at +31dBmV, VOUT = +58dBmV/tone fIN = 33MHz, VOUT = +63dBmV 2ND Harmonic Distortion fIN = 33MHz, VOUT = +60dBmV, TA = 0C to +85C fIN = 65MHz, VOUT = +60dBmV fIN = 22MHz, VOUT = +63dBmV 3RD Harmonic Distortion 1dB Compression Point AM to AM AM to PM Rejection at 135MHz fIN = 22MHz, VOUT = +60dBmV fIN = 65MHz, VOUT = +60dBmV Gain = 26dB, fIN = 65MHz Gain = 28dB, VIN = +34dBmV to +38dBmV, fIN = 65MHz Gain = 28dB, VIN = +34dBmV to +38dBmV, fIN = 65MHz Referenced to 65MHz 36 MIN TYP -55.4 dBc -47.6 -58 -56 -61 -53 -58 -57 22 -0.1 -1.3 47 dBm dB degrees dBc -51 dBc -50 dBc MAX UNITS
Two-Tone Third-Order Distortion
TIMING CHARACTERISTICS
(MAX3507 EV Kit, VCC = +4.75V to +5.25V, VGND = 0, VTXEN = V SHDN = VCC, TA = +25C, unless otherwise specified.) (Note 3)
PARAMETER SEN to SCLK Rise Set Time SEN to SCLK Rise Hold Time SDA to SCLK Setup Time SDA to SCLK Hold Time SDA Pulse-Width High SDA Pulse-Width Low SCLK Pulse-Width High SCLK Pulse-Width Low SYMBOL tSENS tSENH tSDAS tSDAH tDATAH tDATAL tSCLKH tSCLKL CONDITIONS MIN 20 10 10 20 50 50 50 50 TYP MAX UNITS ns ns ns ns ns ns ns ns
Note 1: Note 2: Note 3: Note 4: Note 5:
Guaranteed by design and characterization to 3 sigma for TA < +25C, unless otherwise specified. AC gain correlated to DC gain measurements to 3 sigma. Guaranteed by design and characterization to 6 sigma. All transients comply with DOCSIS 1.1 limits for transmit power ripple of 0.1dB. Does not include output matching; see Output Match in the Applications section.
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter
Typical Operating Characteristics
(MAX3507 EV Kit, VCC = +5.0V, VIN = +34dBmV, TXEN = SHDN = VCC, fIN = 20MHz, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX3507 toc01
MAX3507
SUPPLY CURRENT IN HIGH-POWER MODE vs. OUTPUT POWER
MAX3507 toc02
SUPPLY CURRENT IN LOW-NOISE MODE vs. OUTPUT POWER
NO AC SIGNALS APPLIED TA = +85C SUPPLY CURRENT (mA) 100 90 80 70 60 TA = +25C 110
MAX3507 toc03
250
250 230 210 SUPPLY CURRENT (mA) 190 170 150 130 110 90 TA = -40C TA = +25C TA = +85C NO AC SIGNALS APPLIED
NO AC SIGNALS APPLIED HP MODE, GC = 127
120
200 SUPPLY CURRENT (mA)
150
100
LN MODE, GC = 80
50 TXEN = GND 0 -40 -15 10 35 60 85 TEMPERATURE (C)
70 50 30 40 50 POUT (dBmV)
50 40 70 0 10 20 30 POUT (dBmV)
TA = -40C
60
40
50
60
VOLTAGE GAIN IN HIGH-POWER MODE vs. TEMPERATURE
MAX3507 toc04
VOLTAGE GAIN IN LOW-NOISE MODE vs. TEMPERATURE
MAX3507 toc05
VOLTAGE GAIN IN HIGH-POWER MODE vs. FREQUENCY
GC = 127 GC = 119 GC = 99 GC = 79 GC = 59 -14 -34 -54
MAX3507 toc06
32.2 32.1 32.0 VOLTAGE GAIN (dB) 31.9 31.8 31.7 31.6 31.5 31.4 31.3 31.2 -40 -15 10 35 TEMPERATURE (C) GC = 127 60 VCC = +4.7V VCC = +5.3V VCC = +5.0V
-5.4 -5.6 -5.8 VOLTAGE GAIN (dB)
46 26 VOLTAGE GAIN (dB) 6
-6.0 -6.2 -6.4 -6.6 -6.8 -7.0 -40 -15 10 35 TEMPERATURE (C) GC = 80 60 85 VCC = 4.7V, 5.0V, 5.3V
-74 1 10 100 1000 INPUT FREQUENCY (MHz)
85
VOLTAGE GAIN IN LOW-NOISE MODE vs. FREQUENCY
MAX3507 toc07
VOLTAGE GAIN vs. GAIN CODE
MAX3507 toc08
GAIN STEP IN HIGH-POWER MODE vs. GAIN CODE
0.9 0.8 GAIN STEP (dB) 0.7 0.6 0.5 0.4 0.3 0.2
MAX3507 toc09
26 6 VOLTAGE GAIN (dB) -14 -34 -54 -74 -94 1 10 100 GC = 110 GC = 90 GC = 70 GC = 50
36 26 HIGH-POWER MODE VOLTAGE GAIN (dB) 16 6 -4 -14 -24 -34 LOW-NOISE MODE
1.0
0.1 0 20 40 60 80 GAIN CODE 100 120 140 60 70 80 90 100 110 120 130 GAIN CODE
1000
INPUT FREQUENCY (MHz)
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
Typical Operating Characteristics (continued)
(MAX3507 EV Kit, VCC = +5.0V, VIN = +34dBmV, TXEN = SHDN = VCC, fIN = 20MHz, TA = +25C, unless otherwise noted.)
GAIN STEP IN LOW-NOISE MODE vs. GAIN CODE
MAX3507 toc10
TRANSMIT NOISE vs. GAIN CODE
MAX3507 toc11
TRANSMIT ENABLE/DISABLE TRANSIENT IN HIGH-POWER MODE vs. GAIN CODE
45 40 STEP SIZE (mV) 35 30 25 20 15 ENABLE
MAX3507 toc12
1.0 0.9 0.8 0.7 GAIN STEP (dB) 0.6 0.5 0.4 0.3 0.2 0.1 0 30 40 50 60 70 80
0 -10 HIGH POWER MODE -20 -30 -40 LOW NOISE MODE -50 -60
50
NOISE (dBm/Hz at BW = 160kHz)
10 5 0 DISABLE 60 70 80 90 100 110 120 130
90 100 110 120
30
50
70
90
110
130
GAIN CODE
GAIN CODE
GAIN CODE
TRANSMIT ENABLE/DISABLE TRANSIENT IN LOW-NOISE MODE vs. GAIN CODE
MAX3507 toc13
2ND-ORDER HARMONIC DISTORTION IN HIGH-POWER MODE vs. FREQUENCY
MAX3507 toc14
3RD-ORDER HARMONIC DISTORTION IN HIGH-POWER MODE vs. FREQUENCY
VOUT = 60dBmV -45 HARMONIC DISTORTION (dBc) -50 -55 -60 -65 -70 -75 -80 5 15 25 35 45 55 65
MAX3507 toc15
6 5 TRANSIENT (mVp-p) 4 3 ENABLE 2 1 DISABLE 0 30 50 70 90 110
-40 -45 HARMONIC DISTORTION (dBc) -50 -55 -60 -65 -70 -75 -80
VOUT = 64dBmV
-40
130
5
15
25
35
45
55
65
GAIN CODE
INPUT FREQUENCY (MHz)
INPUT FREQUENCY (MHz)
PASSBAND FLATNESS vs. RC
VCC = +5.0V D7 = 1 GC = 119 R = 301 C = 22pF 0.2dB/ div R = 680 C = 10pF NO EQUALIZATION
MAX3507 toc16
21.6dB
19.6dB 1MHz
6.9MHz/div
70MHz
6
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter
Pin Description
PIN 1 2 3 4, 8, 12, 23, 26 5, 22, 25 6 7 9 10 11 13, 15, 17, 20, 24 14 16 18 19 21 27 28 NAME BIASF DC+ DCGND VCC IN+ INCS SDA SCLK N.C. SHDN CEXT OUTOUT+ TXEN EQ+ EQFilter Bias. Connect to GND. Filter Offset Correction. Connect 0.1F capacitor between this pin and DC-. Filter Offset Correction. Connect 0.1F capacitor between this pin and DC+. Ground +5V Supply. Bypass this pin to GND with a 0.1F capacitor as close to the part as possible. Positive Input. Along with IN-, this port forms a high-impedance differential input to the filter. Negative Input. When not used, this port must be AC-coupled to ground. See IN+. Serial Interface Enable (Chip Select). TTL-compatible input. See Serial Interface section. Serial Interface Data (Serial Data). TTL-compatible input. See Serial Interface section. Serial Interface Clock (Serial Clock). TTL-compatible input. See Serial Interface section. No Connection. Not internally connected. Shutdown. When SHDN is set low, all functions (including the serial interface) are disabled. RF Output Bypass. Bypass to ground with a 0.1F capacitor. Negative Output. Along with OUT+, this port forms a 300 impedance output. This port is matched to a 75 load using a 2:1 (voltage ratio) transformer. Positive Output. See OUT-. Signal Path Enable. Setting this pin low turns off the PGA and power amplifier, leaving the filter and serial interface enabled to save the last gain setting. Positive Equalizer. Connect an RC network if equalization of the filter passband is desired; leave open otherwise. See Typical Operating Characteristics. Negative Equalizer. Connect an RC network if equalization of the filter passband is desired; leave open otherwise. See Typical Operating Characteristics. DESCRIPTION
MAX3507
Detailed Description
Internal Filter
The internal filter consists of an input transconductance amplifier, a balanced fifth-order elliptic active lowpass filter, and an offset-correction feedback network. The signal at the output of the filter is level-shifted into the programmable-gain amplifier. The transconductance amplifier provides a high input impedance to the user, and current drives the filter to minimize insertion loss. The filter is a Gm-C topology to provide sufficient bandwidth and linearity. The cutoff frequency of the filter is fixed at 75MHz, while the specified stopband attenuation is met at 120MHz. The internal offset-correction feedback network removes any DC offset at the output of the filter. An offset voltage at this node would generate a transient during a TX-enable or -disable transition, which would not be acceptable. The offset-correction loop effectively AC-couples the filter output to the programmable-gain
amplifier input. The network generates a highpass corner frequency at: f-3dB(kHz) = 12.5/C(F) Specified performance is achieved when the input is driven differentially. The MAX3507 may be driven single-ended. To drive the device in this manner, one of the input pins must be capacitively coupled to ground. Use a capacitor whose value is large enough to allow for a low-impedance path to ground at the lowest frequency of operation. For operation down to 5MHz, a 0.001F capacitor is suggested.
Programmable-Gain Amplifier
The programmable-gain amplifier (PGA) consists of the variable-gain amplifier (VGA) and the digital-to-analog converter (DAC), which provide better than 55dB of output-level control in 0.5dB steps. The PGA is implemented as a programmable Gilbert-cell attenuator. It uses a differential architecture to achieve maximum linearity. The gain of the PGA is determined by a 7-bit
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
word (D6-D0) programmed through the serial data interface (Tables 1 and 2).
Table 1. Serial-Interface Control Word
BIT 7 (MSB) 6 5 4 3 2 1 0 (LSB) MNEMONIC D7 D6 D5 D4 D3 D2 D1 D0 DESCRIPTION High-Power/Low-Noise Mode Select Gain Code, Bit 6 Gain Code, Bit 5 Gain Code, Bit 4 Gain Code, Bit 3 Gain Code, Bit 2 Gain Code, Bit 1 Gain Code, Bit 0
Equalizer Function
It is possible to add passband amplitude equalization to the MAX3507. This is accomplished by adding polezero peaking to the Gm stage of the PGA. Placing a series RC network between pins EQ+ and EQ- realizes the peaking function. Refer to Typical Operating Characteristics for typical values and the associated degree of equalization.
Power Amplifier
The power amplifier is a Class A differential amplifier capable of driving +64dBmV (QPSK) differentially. This architecture provides superior even-order distortion performance but requires that a transformer be used to convert to a single-ended output. In transmit-disable mode, the output amplifier is shut off. Disabling the output devices also allows the lowest standby noise. To achieve the proper load line, the output impedance of the power amplifier is 300 differential. To match the output impedance to a 75 load, the transformer must have a turns ratio (voltage ratio) of 2:1 (4:1 impedance ratio). The differential amplifier is biased directly from the +5V supply using the center tap of the output transformer. This provides a significant benefit when switching between transmit mode and transmit disable mode. Stored energy due to bias currents will cancel within the transformer and prevent switching transients from reaching the load.
for significantly lower output noise and lower transmit/transmit disable transients. The full range of gain codes (D6-D0) may be used in either mode. For DOCSIS applications, HP mode is recommended for output levels at or above +42dBmV, and LN mode is recommended for output levels below +42dBmV.
Shutdown Mode
In normal operation, the shutdown pin (SHDN) is held high. When SHDN is set low, all circuits within the device are disabled. Only leakage currents flow in this state. Data stored within the serial data interface latches will be lost upon entering this mode. Current consumption is reduced to 1A (typ) in shutdown mode.
Serial Interface
The serial interface has an active-low enable (CS) to bracket the data, with data clocked in MSB first on the rising edge of SCLK. Data is stored in the storage latch on the rising edge of CS. The serial interface controls the gain state of the PGA and the output amplifier. Tables 1 and 2 show the register format. Serial interface timing is shown in Figure 1.
Output Match
The MAX3507 output impedance is internally matched to 300. This 300 internal resistor is placed across the OUT+ and OUT- terminals. When used in conjunction with a 2:1 (voltage ratio) transformer, the MAX3507 output impedance is matched to 75. To improve the output impedance matching for the highend frequency range (65MHz), a reactive match may be employed as part of the ensuing diplex filter. The reactive match normally consists of a series inductor (180nH typ) followed by a shunt capacitor (33pF typ), and is placed directly after the output transformer. This match will also improve the gain flatness substantially. As mentioned above, the matching components may be incorporated into the diplex filter design. Optimize the input impedance of the diplex filter to be 35 + j35 (typ) at 65MHz when using the specified output transformer.
Applications Information
Transmit High-Power and Low-Noise Modes
The MAX3507 has two transmit modes, high-power (HP) mode and low-noise (LN) mode. Each of these modes is controlled by D7 (MSB) of the 8-bit programming word. When D7 is a logical 1, HP mode is enabled. When D7 is a logical 0, LN mode is enabled. Each of these modes is characterized by the activation of a distinct output stage. In HP mode, the output stage exhibits a gain that is 15dB higher than gain in LN mode. In LN mode, the lower gain output stage allows
Transformer
To match the output of the MAX3507 to a 75 load, a 2:1 (voltage ratio) transformer is required. This trans-
8
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
A G B C D E F
D7
D6 A. tSENS B. tSDAS C. tSDAH D. tSCLKL
D5
D4
D3
D2
D1
D0
E. tSCLKH F. tSENH G. tDATAH/tDATAL
Figure 1. Serial Interface Timing Diagram
Table 2. Chip-State Control Bits
SHDN 0 1 1 1 1 1 1 1 1 1 TXEN X 0 1 1 1 1 1 1 1 1 D7 X X 1 0 0 0 0 1 1 1 D6 X X X X 0 1 1 1 1 1 D5 X X X X 1 0 1 0 1 1 D4 X X X X 1 1 0 1 0 1 D3 X X X X 0 0 1 0 1 1 D2 X X X X 0 0 1 1 1 1 D1 X X X X 0 0 1 1 1 0 D0 X X X X 0 0 0 0 0 1 GAIN STATE (DECIMAL) -- -- -- -- 48 80 110 86 110 125 GAIN (dB) -- -- -- -- -22.6 -6.29 8.68 11.69 23.7 31.0 STATES Shutdown Transmit Disable Mode Transmit Enable Mode, High Power Transmit Enable Mode, Low Noise -- -- -- -- -- --
Typical gain at TA = +25C and VCC = +5V.
former must have adequate bandwidth to cover the intended application. Note that most RF transformers specify bandwidth with a 50 source on the primary and a matching resistance on the secondary winding. Operating in a 75 system will tend to shift the low-frequency edge of the transformer bandwidth specification up by a factor of 1.5, due to primary inductance. Keep this in mind when specifying a transformer. Bias to the output stage is provided through the center tap on the transformer primary. This greatly diminishes
the on/off transients present at the output when switching between transmit and transmit disable modes. Commercially available transformers typically have adequate balance between half-windings to achieve substantial transient cancellation. Finally, keep in mind that transformer core inductance varies proportionally with temperature. If the application requires low temperature extremes (less than 0C), adequate primary inductance must be present to sustain low-frequency output capability as temperatures
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
drop. In general, this will not be a problem, as modern RF transformers have adequate bandwidth.
Input Circuit
To achieve rated performance, the inputs of the MAX3507 must be driven differentially with an appropriate input level. The differential input impedance is approximately 4k. The MAX3507 has sufficient gain to produce an output level of +64dBmV (QPSK through a 2:1 transformer) when driven with a +34dBmV input signal. Rated performance is achieved with this input level. When a lower input level is present, the maximum output level will be reduced proportionally and output linearity will increase. If an input level greater than +34dBmV is used, the 3rd-order distortion performance will degrade. If a single-ended source drives the MAX3507, one of the input terminals must be capacitively coupled to ground (IN+ or IN-). The value of this capacitor must be large enough to look like a short circuit at the lowest frequency of interest. For operation at 5MHz with a 75 source impedance, a value of 0.001F will suffice.
pling capacitor at the central power-supply node. The power-supply traces branch out from this node, each going to a separate power-supply node in the circuit. At the end of each of these traces is a decoupling capacitor that provides very low impedance at the frequency of interest. This arrangement provides local power-supply decoupling at each power-supply pin. The powersupply traces must be made as thick as practical. Ground inductance degrades distortion performance. Therefore, ground plane connections to pins 4, 8, 12, 23, and 26 should be made with multiple vias if necessary.
Output Circuit Layout
The differential implementation of the MAX3507's output has the benefit of significantly reducing even-order distortion, the most significant of which is 2nd-harmonic distortion. The degree of distortion cancellation depends on the amplitude and phase balance of the overall circuit. It is important to keep the trace lengths from the output pins equal.
Layout Issues
A well-designed PC board is an essential part of an RF circuit. For best performance pay attention to powersupply layout issues as well as the output circuit layout.
Chip Information
TRANSISTOR COUNT: 1457
Power-Supply Layout
For minimal coupling between different sections of the MAX3507, the ideal power-supply layout is a star configuration. This configuration has a large-value decou-
Pin Configuration
GND
EQ+
GND
N.C.
VCC
28
EQ-
27
26
25
24
23
BIASF DC+ DCGND VCC IN+ IN-
1 2 3 4 5 6 7
22 21 20 19
VCC
TOP VIEW
TXEN N.C. OUT+ OUTN.C. CEXT N.C.
MAX3507
18 17 16 15
10
11
12
13
N.C.
GND
SCLK
GND
10
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SHDN
CS
SDA
14
8
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter
Package Information
MAX3507
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Upstream CATV Amplifier with On-Chip Anti-Alias Filter MAX3507
Package Information (continued)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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