Circuit Note

CN-0279

Circuits from the Lab™ reference circuits are engineered and

tested for quick and easysystemintegrationto helpsolve today’s

analog, mixed-signal, and RF design challenges. For more

informationand/orsupport, visit www.analog.com/CN0279.

Devices Connected/Referenced

AD9642

14-Bit, 250 MSPS Analog-to-Digital Converter

ADL5565

6 GHz Ultrahigh Dynamic Range Differential

Amplifier

High IF Sampling Receiver Front End with Band-Pass Filter

Rev. 0

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EVALUATION AND DESIGN SUPPORT

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The circuit, shown in Figure 1, is a narrow, band-pass receiver

front end based on the ADL5565 ultralow noise differential

amplifier driver and the AD9642 14-bit, 250 MSPS analog-to-

digital converter (ADC).

The third-order, Butterworth antialiasing filter is optimized based

on the performance and interface requirements of the amplifier

and ADC. The total insertion loss due to the filter network and

other components is only 5.8 dB.

The overall circuit has a bandwidth of 18 MHz with a pass-band

flatness of 3 dB. The signal-to-noise ratio (SNR) and spurious-

free dynamic range (SFDR) measured with a 127 MHz analog

input are 71.7 dBFS and 92 dBc, respectively. The sampling

frequency is 205 MSPS, thereby positioning the IF input signal

in the second Nyquist zone between 102.5 MHz and 205 MHz.

CIRCUIT DESCRIPTION

The circuit accepts a single-ended input and converts it to

differential input using a wide bandwidth (3 GHz) Mini-Circuits

TC2-1T 1:2 transformer. The 6 GHz ADL5565 differential

amplifier has a differential input impedance of 200 Ω when

operating at a gain of 6 dB, and 100 Ω when operating at a

gain of 12 dB. A gain option of 15.5 dB is also available.

The ADL5565 is an ideal driver for the AD9642, and the fully

differential architecture through the band-pass filter and into

the ADC provides good high frequency common-mode rejection,

as well as minimizes second-order distortion products. The

ADL5565 provides a gain of 6 dB or 12 dB, depending on the input

connection. In the circuit, a gain of 12 dB was used to compensate

for the insertion loss of the filter network and transformer

(approximately 5.8 dB), providing an overall signal gain of 5.5 dB.

Figure 1. 14-Bit, 250 MSPS Wideband Receiver Front End (Simplified Schematic: All Connections and Decoupling Not Shown)

Gains, Losses, and Signal Levels Measured Values for an Input Frequency of 127 MHz

0.1µF

0.1µF

0.1µF

33pF

36nH

0.1µF

ADL5565

G = 12dB

2.5pF

XFMR

1:2 Z

TC2-1T

INPUT

Z = 50Ω

INTERNAL

INPUT Z

AD9642

14-BIT

205MSPS

ADC

620nH

5Ω

5Ω

187Ω

40Ω

217Ω

+3.3V

+1.8V

DRVDD

+1.8V

AVDD

5.6dB LOSS

0.2dB LOSS

5.8dB LOSS

11.8dB GAIN

FS = 1.75V

p-p DIFF

620nH

0.5dB LOSS

ANALOG

INPUT

+1.5dBm FS

AT 127MHz

OVERALL

GAIN = 5.5dB

100Ω

100Ω

0.1µF

5Ω

5Ω

15Ω

15Ω

2.85kΩ

1.2pF

1.2pF

33pF

VCM

36nH

VIP2

VIN2

VIP1

VIN1