CN-0248

Circuit Note

Rev. 0 | Page 4 of 6

reach its setpoint at as low an input power as when the maximum

gain code was 11. This allows VGA2 to keep its setpoint at

higher input powers, thus allowing the handoff from VGA2 to

VGA1 to take place before VGA2 runs out of gain. This ensures

that the signal level applied to the ADRF6510 is maintained at a

constant level until the uppermost of the input power range.

Figure 6 compares the EVM between the minimum and the

maximum digital gain settings (both VGAs were set to either

a gain code of 11 or a gain code of 00) on the ADL5336 VGAs;

however, the VGA1 and VGA2 setpoints were 707 mV rms and

88 mV rms, respectively.

0

–50

–95

35

PIN (dBm)

–45

–40

–35

–30

–25

–20

–15

–10

–5

–85 –75 –65 –55 –45 –35 –25 –15

–5

5

15

25

GAIN = 11

GAIN = 00

Figure 6. System EVM with VGA1 Setpoint = 707 mV rms and

VGA2 Setpoint = 88 mV rms

The same dynamics are occurring in Figure 6 as they were

in Figure 5, only they are much more exaggerated. When the

maximum gain code is 00, VGA2 reaches its setpoint at around

−40 dBm input power. It maintains its setpoint until about

−10 dBm, at which point, VGA1 has not reached its setpoint

of 707 mV rms. VGA1 does not reach its setpoint until about

0 dBm, and the EVM starts to level off somewhat. When the

maximum gain is set to 11, this same behavior happens again;

however, VGA2 maintains its setpoint only to about −20 dBm

because there is more gain available to attain the prescribed

setpoints.

COMMON VARIATIONS

System and Synthesizer

The signal generator that provides the 2×LO for the ADL5387

can be replaced by a wideband synthesizer, such as the ADF4350,

which has an integrated VCO. The ADF4350 belongs to a family

of synthesizers that operate over a wide frequency range, from

135 MHz to 4350 MHz, and that has varying phase noise and

output power metrics, making it easy to find the device to

match the required specifications of the application.

System and ADC

Adding an ADC to the system to sample the I and Q signals of

the ADRF6510 is a natural progression to complete the analog

signal chain. A dual ADC, such as the AD9248, provides 14 bits

of resolution and is offered in 20 MSPS, 40 MSPS, or 65 MSPS

sampling rates. An antialiasing filter is recommended between

the output of the ADRF6510 and the AD9248. Refer to the

ADRF6510 data sheet for the antialiasing filter design example.

ADRF6510 Output Common-Mode Voltage Considerations

The ADRF6510 output common-mode voltage is adjustable from

1.5 V to 3.0 V without loss of drive capability. Many modern ADCs

have input common-mode voltages of less than 1.5 V. Driving

the VOCM pin to an output common-mode voltage less than 1.5 V

starts to degrade the distortion performance of the ADRF6510;

however, it is still functional for less than 1.5 V common-mode

voltage levels. To maintain distortion performance, a dc level

shifting circuit may be required, or an integrated filter and

VGA device with a lower common-mode voltage, such as the

ADRF6516, can be used.

CIRCUIT EVALUATION AND TEST

Equipment Needed/Used

Signal generators include the following:

• Agilent E4438C vector signal generator

• Agilent E4438C signal generator

The baseband signal capture device is the

• Agilent DSO90604A oscilloscope

The EVM computation device(s) include the following:

• Agilent 89600 VSA software

• PC running Windows XP connected to oscilloscope via a

USB cable

The power supply includes the following:

• ±5 V supply. All boards require +5 V with the exception

of the AD8130 boards that require ±5 V

The evaluation boards include the following:

• ADL5336-EVALZ (one required)

• ADL5387-EVALZ (one required)

• ADRF6510-EVALZ (one required)

• AD8130-EBZ (two required)