LT5516

10

5516f

APPLICATIO S I FOR ATIO

I-Channel and Q-Channel Outputs

Each of the I-channel and Q-channel outputs is internally

or AC coupled to the external loads. The differential output

impedance of the demodulator is 120

Ω in parallel with a

5pF internal capacitor, forming a lowpass filter with a

ended load resistance) should be larger than 600

Ω to

assure full gain. The gain is reduced by 20 • log(1 + 120

Ω/

each output pin is connected to a 50

Ω load (100Ω differ-

ential load). The output should be taken differentially (or

by using differential-to-single-ended conversion) for best

RF performance, including NF and IM2.

The phase relationship between the I-channel output sig-

nal and Q-channel output signal is fixed. When the LO

input frequency is larger (or smaller) than the RF input

When AC output coupling is used, the resulting highpass

filter’s –3dB roll-off frequency is defined by the R-C

Care should be taken when the demodulator’s outputs are

DC coupled to the external load, to make sure that the I/Q

mixers are biased properly. If the current drain from the

outputs exceeds 6mA, there can be significant degrada-

tion of the linearity performance. Each output can sink no

more than 13mA when the outputs are connected to an

The I/Q output equivalent circuit is shown in Figure 7.

3

2

RF

J1

T1

LDB31900M20C-416

LT5516

5516 F05

1k

1.54V

1.54V

L1

33nH

6

2

4

1

3

C1

1nF

Figure 5. RF Input Equivalent Circuit with External Matching