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MAX11014BGTM+中文资料

General Description

The MAX11014/MAX11015 set and control bias condi-tions for dual MESFET power devices found in point-to-point communication and other microwave base stations. The MAX11014 integrates complete dual ana-log closed-loop drain-current controllers for Class A MESF ET amplifier operation, while the MAX11015 tar-gets Class AB operation. Both devices integrate SRAM lookup tables (LUTs) that can be used to store temper-ature and drain-current compensation data.

Each device includes dual high-side current-sense amplifiers to monitor the MESFET drain currents through the voltage drop across the sense resistors in the 0 to 625mV range. External diode-connected transistors mon-itor the MESFET temperatures while an internal tempera-ture sensor measures the local die temperature of the MAX11014/MAX11015. The internal DAC sets the volt-ages across the current-sense resistors by controlling the GATE voltages. The internal 12-bit SAR ADC digitizes internal and external temperature, internal DAC voltages,current-sense amplifier voltages, and external GATE volt-ages. Two of the 11 ADC channels are available as gen-eral-purpose analog inputs for analog system monitoring.The MAX11014’s gate-drive amplifier functions as an integrator for the Class A drain-current control loop while the MAX11015’s gate-drive amplifier functions with a gain of -2 for Class AB applications. The current-limited gate-drive amplifier can be fast clamped to an external voltage independent of the digital input from the serial interface. Both the MAX11014 and the MAX11015 include self-calibration modes to minimize error over time, temperature, and supply voltage.

The MAX11014/MAX11015 feature an internal reference and can operate from separate ADC and DAC external references. The internal reference provides a well-regu-lated, low-noise +2.5V reference for the ADC, DAC, and temperature sensors. These integrated circuits operate from a 4-wire 20MHz SPI?-/MICROWIRE?-compatible or 3.4MHz I 2C-compatible serial interface (pin-selec-table). Both devices operate from a +4.75V to +5.25V analog supply (2.8mA typical supply current), a +2.7V to +5.25V digital supply (1.5mA typical supply current),and a -4.5V to -5.5V negative supply (1.1mA supply current). The MAX11014/MAX11015 are available in a 48-pin thin QF N package specified over the -40°C to +105°C temperature range.

Features

?Dual Drain-Current-Sense Gain Amplifier

Preset Gain of 4

±0.5% Accuracy for Sense Voltages Between 75mV and 625mV (MAX11014)?Common-Mode Sense-Resistor Voltage Range

0.5V to 11V (MAX11014)

5V to 32V (MAX11015)

?Low-Noise Output GATE Bias with ±10mA GATE Drive ?Fast Clamp and Power-On Reset

?12-Bit DAC Controls MESFET GATE Voltage ?Internal Temperature Sensor/Dual Remote Diode Temperature Sensors ?Internal 12-Bit ADC Measures Temperature and Voltage ?Pin-Selectable Serial Interface

3.4MHz I 2C-Compatible Interface

20MHz SPI-/MICROWIRE-Compatible Interface

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

________________________________________________________________Maxim Integrated Products 1

Ordering Information

Applications

For pricing delivery, and ordering information please contact Maxim Direct at 1-888-629-4642,or visit Maxim’s website at https://www.wendangku.net/doc/0417615425.html,.

SPI is a trademark of Motorola, Inc.

MICROWIRE is a trademark of National Semiconductor Corp.

*Future product—contact factory for availability.**EP = Exposed pad.

Note:All devices are specified over the -40°C to +105°C operating temperature range.

Pin Configuration and Typical Operating Circuit appear at end of data sheet.

Cellular Base-Station RF MESFET Bias Controllers Point-to-Point or Point-to-Multipoint Links Industrial Process Control

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 2_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

ELECTRICAL CHARACTERISTICS

(V GATEVSS = V AVSS = -5.5V to -4.75V, V AVDD = +4.75V to +5.25V, V DVDD = +2.7V to V AVDD , external V REFADC = +2.5V, external V REFDAC = +2.5V, C REFADC = C REFDAC = 0.1μF, V OPSAFE1 = V OPSAFE2 = 0, V RCS1+ = V RCS2+= +5V, C FILT1= C FILT3 = 1nF, C FILT2 =

AV DD to AGND.........................................................-0.3V to +6V DV DD to DGND.........................................................-0.3V to +6V AGND to DGND.....................................................-0.3V to +0.3V AV SS to AGND...........................................................-0.3V to -6V RCS1+, RCS1-, RCS2+, RCS2- to GATEV SS

(MAX11014)........................................................-0.3V to +13V RCS1+, RCS1-, RCS2+, RCS2- to AGND

(MAX11015)........................................................-0.3V to +34V RCS1- to RCS1+.......................................................-6V to +0.3V RCS2- to RCS2+.......................................................-6V to +0.3V GATEV SS to AGND...................................................+0.3V to -6V GATE1, GATE2 to AGND.....(GATEV SS - 0.3V) to (AV DD + 0.3V)DV DD to AV DD ..........................................-0.3V to (AV DD + 0.3V)All Other Analog Inputs to AGND............-0.3V to (AV DD + 0.3V)

PGAOUT1, PGAOUT2 to AGND..............-0.3V to (AV DD + 0.3V)SCLK/SCL, DIN/SDA, CS /A0, N.C./A2, CNVST , OPSAFE1,

OPSAFE2 to DGND.............................-0.3V to (DV DD + 0.3V)DOUT/A1, SPI/I2C , ALARM, BUSY

to DGND..............................................-0.3V to (DV DD + 0.3V)Maximum Current into Any Pin............................................50mA Continuous Power Dissipation (T A = +70°C)48-Pin Thin QFN (derate 27.0mW/°C

above +70°C)..........................................................2162.2mW Operating Temperature Range .........................-40°C to +105°C Storage Temperature Range ...............................-60°C to 150°C Junction Temperature......................................................+150°C Lead Temperature (soldering, 10s).................................+300°C

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

_______________________________________________________________________________________3

ELECTRICAL CHARACTERISTICS (continued)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 4_______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

_______________________________________________________________________________________5

ELECTRICAL CHARACTERISTICS (continued)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 6_______________________________________________________________________________________

SPI-INTERFACE TIMING CHARACTERISTICS

I C-INTERFACE SLOW-/FAST-MODE TIMING CHARACTERISTICS

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

_______________________________________________________________________________________7

I 2C-WIRE-INTERFACE HIGH-SPEED-MODE TIMING CHARACTERISTICS

(Note 9) (See Figure 3.)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 8_______________________________________________________________________________________

MISCELLANEOUS TIMING CHARACTERISTICS

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

_______________________________________________________________________________________9

Note 1:All current-sense amplifier specifications are tested after a current-sense calibration (valid when drain current = 0mA). See

RCS Error vs. GATE Current in the Typical Operating Characteristics . The calibration is valid only at one temperature and supply voltage and must be repeated if either the temperature or supply voltage changes.

Note 2:The hardware configuration register’s CH_OCM1 and CH_OCM0 bits are set to 0. See Table 10a. The max specification is

limited by tester limitations.

Note 3:Guaranteed by design. Not production tested.

Note 4:At power-on reset, the output safe switch is closed. See the ALMHCFG (Read/Write)section.

Note 5:Integral nonlinearity is the deviation of the analog value at any code from its theoretical value after the gain and offset errors

have been calibrated out.

Note 6:Offset nulled.

Note 7:Absolute range for analog inputs is from 0 to V AVDD .

Note 8:Device and sensor at the same temperature. Verified by the current ratio (see the Temperature Measurements section).Note 9:All timing specifications referred to V IH or V IL levels.

Note 10:D OUT goes into tri-state mode after the CS rising edge. Keep CS low long enough for the DOUT value to be sampled

before it goes to tri-state.

Note 11:A master device must provide a hold time of at least 300ns for the SDA signal (referred to V IL of the SCL signal) to bridge

the undefined region of SCL’s falling edge.

Note 12:t R and t F measured between 0.3 x DV DD and 0.7 x DV DD .

Note 13:C B = total capacitance of one bus line in pF. For bus loads between 100pF and 400pF, the timing parameters should be

linearly interpolated.

Note 14:An appropriate bus pullup resistance must be selected depending on board capacitance. For more information, refer to the

I 2C documentation on the Philips website.

Note 15:Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.

Note 16:When a command is written to the serial interface, it is passed to the internal oscillator clock to be executed. There is a

small synchronization delay before the new value is written to the appropriate register. If the user attempts to read the new value back before t RDBK , no harm will be caused to the data, but the read command may not yet show the new value.

Note 17:This is the minimum time from the end of a command before CNVST should be asserted. The time allows for the data from

the preceding write to arrive and set up the chip in preparation for the CNVST . The time need only be observed when the write affects the ADC controls. Failure to observe this time may lead to incorrect conversions (for example, conversion of the wrong ADC channel).

MISCELLANEOUS TIMING CHARACTERISTICS (continued)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 10______________________________________________________________________________________

Figure 3. High-Speed Timing Diagram

Figure 1. SPI Serial-Interface Timing Diagram

Figure 2. Slow-/Fast-Speed Timing Diagram

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

______________________________________________________________________________________11

02.5

4.0

3.0

3.5

4.5

5.0

5.5

DIGITAL SUPPLY CURRENT vs. DIGITAL SUPPLY VOLTAGE

DV DD SUPPLY VOLTAGE (V)

D V D D S U P P L Y C U R R

E N T (m A )

2.40

2.41

2.43

2.42

2.44

2.45ANALOG SUPPLY CURRENT vs. ANALOG SUPPLY VOLTAGE

M A X 11014 t o c 02

AV DD SUPPLY VOLTAGE (V)

A V D D S U P P L Y C U R R E N T (m A )

4.750

5.000

4.875

5.125

5.250

-0.4

-0.20

0.20.4

RCS ERROR vs. TEMPERATURE

TEMPERATURE (°C)

R C S E R R O R (m V )

-50

-25

100

125

40μs/div

-5V

MAX11014 toc04

V GATE 1V/div

GATE VOLTAGE POWER-UP

0200100

4003005006000

500

FILT1/FILT3 SETTLING TIME vs. FILT1/FILT3 CAPACITIVE LOAD

CAPACITIVE LOAD (pF)

S E T T L I N G T I M E (μs )

200

100

300

400

0.50

0.250

-0.25

-0.50

-10

-5

RCS ERROR vs. GATE CURRENT

GATE CURRENT (mA)

R C S E R R O R (m V

)

0-5

-3

-4

-2

-1

V GATE (V)

G A T E O U T P U T R E S I S T A N C E (?)

GATE OUTPUT RESISTANCE

vs. GATE VOLTAGE

1μs/div

FILT11mV/div

AC-COUPLED

MAX11014 toc08

GLITCH IMPULSE

-1.00

-0.75

-0.50-0.2500.250.500.751.00

1024

20483072

4096

DAC INTEGRAL NONLINEARITY

vs. OUPUT CODE

OUTPUT CODE

D A C I N L (L S B )

Typical Operating Characteristics

(V GATEVSS = -5.5V; V AVDD = V DVDD = +5V, GATEV SS = AV SS = -5V, external V REFADC = +2.5V; external V REFDAC = +2.5V; C REF =0.1μF; T A = T MIN to T MAX , unless otherwise noted.)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 12______________________________________________________________________________________

Typical Operating Characteristics (continued)

(V GATEVSS = -5.5V; V AVDD = V DVDD = +5V, GATEV SS = AV SS = -5V, external V REFADC = +2.5V; external V REFDAC = +2.5V; C REF =0.1μF; T A = T MIN to T MAX , unless otherwise noted.)

-1.00

-0.75-0.50-0.2500.250.500.751.000

1024

20483072

4096DAC DIFFERTIAL NONLINEARITY

vs. OUTPUT CODE

OUTPUT CODE

D A C D N L (L S B

)

-1.00

-0.75-0.50-0.2500.250.500.751.0001024204830724096ADC INTEGRAL NONLINEARITY

vs. OUTPUT CODE

OUTPUT CODE

A D C I N L (L S B

)

-1.00

-0.75-0.50-0.25

00.250.500.751.00

01024204830724096

ADC DIFFERENTIAL NONLINEARITY

vs. OUTPUT CODE

OUTPUT CODE

A D C D N L (L S B

)

6070

75800.1

101

100

1000

ADC SINAD vs. FREQUENCY

FREQUENCY (kHz)

S I N A D (d B )

1000.1

101

100

1000

ADC SFDR vs. FREQUENCY

FREQUENCY (kHz)

S F D R (d B )

0.001

0.01

0.1

101

100

1000

ADC TOTAL HARMONIC DISTORTION

vs. FREQUENCY

FREQUENCY (kHz)

T H D (%)

-120

-80-100-40-60-2000

ADC FFT PLOT

ANALOG INPUT FREQUENCY (kHz)A M P L I T U D E (d B )

f ANALOG_IN = 9.982kHz f CLK = 3.052MHz SINAD = 71.28dBc SNR = 71.51dBc THD = -84.18dBc SFDR = -86.94dBc

0.1

100

1000

DIGITAL SUPPLY CURRENT vs. SAMPLING RATE

SAMPLING RATE (ksps)

D V D D S U P P L Y C U R R

E N T (m A )

2.5026

2.5024

2.5022

2.5020

2.5018

4.750

5.0004.875 5.125 5.250

ADC INTERNAL REFERENCE VOLTAGE

vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

A D C R E F E R E N C E V O L T A G E (V )

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

______________________________________________________________________________________13

2.5018

2.5016

2.50142.5012

2.5010

4.750

5.000

4.875

5.125

5.250

DAC INTERNAL REFERENCE VOLTAGE

vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

D A C R

F E R E N C E V O L T A

G E (V ) 2.48

2.49

2.50

2.51

2.52INTERNAL REFERENCE VOLTAGE

vs. TEMPERATURE

TEMPERATURE (°C)

R E F E R E N C E V O L T A G E (V )

-50

-25

100

125

2.0

1.5

1.0

0.5

04.750

5.0004.875 5.125 5.250

ADC OFFSET ERROR

vs. ANALOG SUPPLY VOLTAGE

AV DD (V)

A D C O F F S E T E R R O R (L S

B )

4ADC OFFSET ERROR vs. TEMPERATURE

M A X 11014 t o c 22

TEMPERATURE (°C)

A D C O F F S E T E R R O R (L S

B )

-50

-25

100

125

01.00.5

2.01.52.5

3.0

4.750

5.0004.875 5.125 5.250ADC GAIN ERROR

vs. ANALOG SUPPLY VOLTAGE

M A X 11014 t o c 23

AV DD (V)

A D C G A I N E R R O R (L S

B )

-3

-1-210324-50025-255075100125

ADC GAIN EROR vs. TEMPERATURE

M A X 11014 t o c 24

TEMPERATURE (°C)

A D C G A I N E R R O R (L S

B )

INTERNAL TEMPERATURE SENSOR ERROR

vs. TEMPERATURE

M A X 11014

t o c 25

-1.00

-0.75-0.25-0.500.500.750.2501.00I N T E R N A L T

E M P E R A T U R E S E N S O R E R R O R (°C )

-50

-25

75100

125

TEMPERATURE (°C)

GND

V RCS1-100mV/div V PGAOUT1200mV/div V FILT1

200mV/div 0 TO 100mV V SENSE TRANSIENT RESPONSE

10ms/div GND

GND

V RCS1-200mV/div V PGAOUT1500mV/div V FILT1

500mV/div 0 TO 250mV V SENSE TRANSIENT RESPONSE

10ms/div

Typical Operating Characteristics (continued)

(V GATEVSS = -5.5V; V AVDD = V DVDD = +5V, GATEV SS = AV SS = -5V, external V REFADC = +2.5V; external V REFDAC = +2.5V; C REF =0.1μF; T A = T MIN to T MAX , unless otherwise noted.)

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 14______________________________________________________________________________________

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

______________________________________________________________________________________15

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers 16______________________________________________________________________________________

Detailed Description

The MAX11014/MAX11015 set and monitor the bias con-ditions for dual MESFET power devices found in cellular base stations and point-to-point microwave links. The internal DAC sets the voltage across the current-sense resistor by controlling the GATE voltage. These devices integrate a 12-bit ADC to measure voltage, internal and external temperature, and communicate through a 4-wire 20MHz SPI-/MICROWIRE-compatible serial interface or 2-wire 3.4MHz I 2C-compatible serial interface (pin-selectable).

The MAX11014/MAX11015 operate from an internal +2.5V reference or individual ADC and DAC external references. The external current-sense resistors moni-tor voltages over the 0 to (V DACREF / 4) range. Two cur-rent-sense amplifiers with a preset gain of four monitor the voltage across the sense resistors. The MAX11014/MAX11015 accurately measure their inter-nal die temperature and two external remote diode tem-perature sensors. The remote pn junctions are typically the base-emitter junction of an npn transistor, either discrete or integrated on a CPU, FPGA, or ASIC.

The MAX11014/MAX11015 also feature an ALARM out-put that can be triggered during an internal or external overtemperature condition, an excessive current-sense voltage, or an excessive GATE voltage. Figure 4 shows the MAX11014’s functional diagram.

The MAX11014 integrates complete dual analog closed-loop drain-current controllers for Class A MESFET amplifier operation. See the MAX11014 Class A Control Loop section. The analog control loop sets the drain current through the current-sense resistors.The MESF ET gate-drive amplifier can vary the DAC code accordingly if the temperature or other system variables change.

Implement Class A amplifier operation with the follow-ing three steps:1)Characterization

Characterize the MESFET over temperature to deter-mine the amplifier’s set of drain-current values,assuming the part-to-part calibration curve is consis-tent. There may be an offset shift, but no important change in the shape of the function. Load these val-ues into the MAX11014 LUTs at power-up. In opera-tion, there is a linear interpolation between the values stored in the LUTs.

Adjust the drain current for other variables such as output power or drain voltage by loading values into the numerical KLUTs.

2)Calibration

In production of the power amplifier, measure the quiescent drain current at a fixed calibration temper-ature (probably room) and adjust the V SET(CODE)value until the drain current is within the specified limits for that temperature. The V SET(CODE)value is stored for loading after power-up. Prior to operation,command a PGA calibration after powering up by writing to the PGA calibration control register, setting the TRACK bit to 0 and the DOCAL bit to 1 (see Table 18).3)Operation

Upon request, the MAX11014 measures the temper-ature of the MESFET and compares it with the previ-ous reading. If the temperature reading has changed, the MAX11014 reads the LUTs with the characterization data and updates the DAC to cor-rect the drain current. Setting the TRACK, DOCAL,and SELFTIME bits to 1 in the PGA calibration con-trol register starts automatic monitoring and adjust-ment of drain current for variations in temperature.Also, if the KLUTs are used, their values are monitored for changes.A DAC correction is then made if necessary.F or Class AB operation with the MAX11015, measure the MESF ET temperature and set the GATE_ voltage through the LUTs and DAC to control the drain current.See the MAX11015 Class AB Control section.Implement Class AB amplifier operation with the same three steps as Class A operation, with the exception that the LUTs set the GATE_ voltage for constant drain current with varying temperature.

Power-On Reset

On power-up, the MAX11014/MAX11015 are in full power-down mode (see the SHUT (Write)section). To change to normal power mode, write two commands to the shutdown register. Set the F ULLPD bit to 0 (other bits in the shutdown register are ignored) on the first command. A second command to this register then activates the internal blocks.

MAX11014 Class A Control Loop

The MAX11014 is designed to set and continuously control the drain current for MESF ET power amplifiers configured to operate in Class A. Set the DAC code to control the voltage across the RCS_+ and RCS_- cur-rent-sense resistor connections. The MAX11014 inter-nal control loop automatically keeps the voltage across the current-sense resistor to the value set by the DAC.See the 12-Bit DAC section.

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

______________________________________________________________________________________

Figure 4. Functional Diagram

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers

18______________________________________________________________________________________

Once the control loop has been set, the MAX11014automatically maintains the drain-current value. F igure 5 details the amplifiers that bias the channel 1 and channel 2 control loops.

The dual current-sense amplifiers amplify the voltage between RCS_+ and RCS_- by four and add an offset voltage (+12mV nominally). These current-sense ampli-fiers amplify sense voltages between 0 and 625mV when V REFDAC = +2.5V. See the Current-Sense Amplifiers section.

The current-sense amplifier output injects a scaled-down replica of the MESF ET drain current at the summing node to complete the internal analog feedback loop. The summing node drives the gate-drive amplifier through a 100k ?series resistor. The gate-drive amplifier is config-ured as an integrator by the external capacitor connect-ed between GATE1/GATE2 and F ILT2/F ILT4. The gate-drive amplifier includes automatic offset cancella-tion between 0 and 24mV to null the 12mV offset from the current-sense amplifier. See the Register Descriptions and PGACAL (Write)sections.

The MAX11014’s analog control loop setpoint is described by the following equation:

where:

V FILT (CODE = 000h) = V FILT1(channel 1) and V FILT3(channel 2) when the THRUDAC1/THRUDAC2 register code is set to 000h.

V FILT = V FILT1(channel 1) and V FILT3(channel 2).

V RCS+ - V RCS-= the voltage drop across the current-sense resistor.

Connect a capacitor from F ILT2 to GATE1 to form an integrator (setting the control-loop dominant pole) with the channel 1 internal 100k ?resistor. Connect a capacitor from F ILT4 to GATE2 to form an integrator (setting the control-loop dominant pole) with the chan-nel 2 internal 100k ?resistor. The gate-drive amplifier’s output drives the MESF ET gates. See the Gate-Drive Amplifiers section.

The channel 1 DAC voltage is output to FILT1 through a series 580k ?resistor. The channel 2 DAC voltage is output to F ILT3 through a series 580k ?resistor.Connect a capacitor from FILT1 to AGND and FILT3 to AGND to set the filter’s time constant for the respective channel.

MAX11015 Class AB Control

The MAX11015 is designed to be used with a Class AB amplifier configuration to independently measure the drain current and set the GATE_ output voltages through the serial interface. After sensing the drain current with no RF signal applied, set the DAC code to obtain the desired GATE_ voltage. F igure 6 details the amplifiers that bias the channel 1 and channel 2 control.

The MAX11015 internal 12-bit DAC voltage is applied to the gate-drive amplifier, which has a preset gain of -2. See the Gate-Drive Amplifiers section. Setting the DAC code between FFFh and 000h typically produces a GATE_ voltage between 0 and (-2 x V REFDAC ). See the HCFG (Read/Write)section for details on adjusting the GATE_ maximum voltage.

The dual current-sense amplifiers amplify the voltage between RCS_+ and RCS_- by four and add an offset voltage (+12mV nominally). The current-sense ampli-fiers amplify sense voltages between 0 and 625mV when V REFDAC = +2.5V. See the Current-Sense Amplifiers section.

Current-Sense Amplifiers

The dual current-sense amplifiers amplify the voltage between RCS_+ and RCS_- and add an offset voltage.Connect a resistor between RCS_+ and RCS_- to sense the MESFET drain current. The current-sense amplifiers scale the sense voltage by four. These amplifiers also reject the drain supply voltage that appears as a DC common-mode level on the current signal.

The gate-drive amplifier includes automatic offset can-cellation between 0 and 24mV to null the 12mV offset from the current-sense amplifier. See the PGACAL (Write)section.

Gate-Drive Amplifiers

The gate-drive amplifiers control the MESFET gate bias settings. The MAX11014’s channel 1 and channel 2DAC voltages are routed through a summing node and into the gate-drive amplifiers. The MAX11015’s channel 1 and channel 2 DAC voltages are routed directly to the gate-drive amplifiers, which have a preset gain of -2.See the 12-Bit DAC section for details on setting the

DAC codes.

MAX11014/MAX11015

Automatic RF MESFET Amplifier

Drain-Current Controllers

______________________________________________________________________________________

Figure 5. MAX11014 Class A Analog Control Loop

M A X 11014/M A X 11015

Automatic RF MESFET Amplifier Drain-Current Controllers