Preliminary

Technical Data

AD8339

Rev. PrA | Page 11 of 15

current mirror. An external transimpedance amplifier is needed

to convert the I and Q outputs to voltages.

Table 4. Phase Select Code for Channel-to-Channel Phase

Shift

φ-Shift

PHx3 (MSB)

PHx2

PHx1

PHx0 (LSB)

0º

0

0

0

0

22.5º

0

0

0

1

45º

0

0

1

0

67.5º

0

0

1

1

90º

0

1

0

0

112.5º

0

1

0

1

135º

0

1

1

0

157.5º

0

1

1

1

180º

1

0

0

0

202.5º

1

0

0

1

225º

1

0

1

0

247.5º

1

0

1

1

270º

1

1

0

0

292.5º

1

1

0

1

315º

1

1

1

0

337.5º

1

1

1

1

DYNAMIC RANGE AND NOISE

Figure 2 is an interconnection block diagram of two channels

(1/2 of the AD8339), more channels are easily added to the

summation (up to 16 when using an AD8021 as the summation

amplifier) by wire-or connecting the outputs as shown for two

channels. For optimum system noise performance, the RF

input signal is provided by a very low noise amplifier such as

the LNA of the AD8332/AD8334 or the preamplifier of the

AD8335. In beamformer applications, the I and Q outputs of a

number of receiver channels are summed (for example, the two

channels illustrated in Figure 2). The dynamic range of the

number of channels (assuming random uncorrelated noise.)

The noise in the two channel example of Figure 2 is increased

by 3 dB while the signal doubles (+6 dB), yielding an aggregate

SNR improvement of (+6 − 3) = +3 dB. For four channels the

dynamic range will increase by +6 dB and so on.

Judicious selection of the RF amplifier ensures the least

degradation in dynamic range. The input referred spectral

TBD

nV/√Hz. For the noise of the AD8339 to degrade the

system noise figure (NF) by 1 dB, the combined noise of the

source and the LNA should be about twice that of the AD8339

than 1 dB. For example, if the noise contribution of the LNA

degradation is 3 dB. If the circuit noise preceding the AD8339 is

degradation is 2 dB. For a circuit noise 1.45× that of the

To determine the input referred noise it is important to know the

Typical filter values for a single channel are 1.58 kΩ and 1 nF, and

implement a 100 kHz single-pole LPF. In the case that two channels

are summed as is done on the evaluation board, the values would

be the same as for a single channel of the AD8333, namely 787 Ω

and 2.2 nF.

If the RF and LO are offset by 10 kHz, the demodulated signal is 10

kHz and is passed by the LPF. The single-channel mixing gain,

from the RF input to the AD8021 output (for example, I1´, Q1´) is

output. Since the AD8021, including the 1.58 kΩ feedback resistor,

contributes another 6.3 nV/√Hz, the total output referred noise is

filter resistor while maintaining the corner frequency, thereby

increasing the gain. The factor limiting the magnitude of the gain is

the output swing and drive capability of the op-amp selected for the

I-to-V converter, in this instance the AD8021.

Because any amplifier has limited drive capability there will be a

finite number of channels that can be summed. This is explained in

great detail in the section below called – Channel Summing.