LT5515 データシートの表示（PDF） - Linear Technology
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LT5515 Datasheet PDF : 12 Pages
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LT5515
APPLICATIO S I FOR ATIO
Table 2 shows the differential input impedance of the LO
input port.
Table 2. LO Input Differential Impedance
FREQUENCY DIFFERENTIAL INPUT
DIFFERENTIAL S11
(GHz)
IMPEDANCE (Ω)
MAG
ANGLE (˚)
1.5
69.3-j59.4
0.469
– 45.8
1.6
64.3-j56.4
0.457
– 49.8
1.7
60.0-j52.7
0.440
– 53.9
1.8
56.4-j48.9
0.421
– 58.0
1.9
53.7-j44.9
0.399
– 62.2
2.0
51.4-j41.2
0.377
– 66.1
2.1
49.8-j37.5
0.352
– 69.9
2.2
48.6-j34.2
0.328
– 73.3
2.3
47.8-j31.0
0.303
– 76.5
2.4
47.3-j28.2
0.279
– 79.5
2.5
46.9-j25.6
0.257
– 82.3
I-Channel and Q-Channel Outputs
Each of the I-channel and Q-channel outputs is internally
connected to VCC though a 60Ω resistor. The output DC
bias voltage is VCC – 0.85V. The outputs can be DC coupled
or AC coupled to the external loads. The differential output
impedance of the demodulator is 120Ω in parallel with a
5pF internal capacitor, forming a lowpass filter with a
–3dB corner frequency at 260MHz. RLOAD (the single-
ended load resistance) should be larger than 600Ω to
assure full gain. The gain is reduced by 20 • log(1 + 120Ω/
RLOAD) in dB when the differential output is terminated by
RLOAD. For instance, the gain is reduced by 6.85dB when
each output pin is connected to a 50Ω 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
frequency, the Q-channel outputs (QOUT+, QOUT–) lead (or
lag) I-channel outputs (IOUT+, IOUT–) by 90°.
When AC output coupling is used, the resulting highpass
filter’s –3dB roll-off frequency is defined by the R-C
constant of the blocking capacitor and RLOAD, assuming
RLOAD > 600Ω.
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 each
output exceeds 6mA, there can be significant degradation
of the linearity performance. Each output can sink no more
than 14mA when the outputs are connected to an external
load with a DC voltage higher than VCC – 0.85V. The I/Q
output equivalent circuit is shown in Figure 7.
LT5515
VCC
J1
RF
T1
LDB311G9020C-452
2
6
1
3
4
RF+
2
L1
10nH
RF–
3
C1
1nF
1k
1.54V
NOTE: NO CONNECTION REQUIRED
ACCORDING TO BALUN TRANSFORMER
MANUFACTURER
5515 F05
Figure 5. RF Input Equivalent Circuit with External Matching at 1.9GHz
5515fa
9
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