THS6062 Datasheet, PDF (22/31 Pages) Texas Instruments – LOW-NOISE ADSL DUAL DIFFERENTIAL RECEIVER

THS6062
LOW-NOISE ADSL DUAL DIFFERENTIAL RECEIVER
SLOS228B – JANUARY 1999 – REVISED JUNE 1999
APPLICATION INFORMATION
optimizing frequency response
Internal frequency compensation of the THS6062 was selected to provide very wide bandwidth performance
and still maintain a very low noise floor. In order to meet these performance requirements, the THS6062 must
have a minimum gain of 2 (–1). Because everything is referred to the noninverting terminal of an operational
amplifier, the noise gain in a G = –1 configuration is the same as in a G = 2 configuration.
One of the keys to maintaining a smooth frequency response, and hence, a stable pulse response, is to pay
particular attention to the inverting terminal. Any stray capacitance at this node causes peaking in the frequency
response (see Figure 42 and Figure 43). There are two things that can be done to help minimize this effect. The
first is to simply remove any ground planes under the inverting terminal of the amplifier. This also includes the
trace that connects to this terminal. Additionally, the length of this trace should be minimized. The capacitance
at this node causes a lag in the voltage being fed back due to the charging and discharging of the stray
capacitance. If this lag becomes too long, the amplifier will not be able to correctly keep the noninverting terminal
voltage at the same potential as the inverting terminal’s voltage. Peaking and possibly oscillations will then
occur.
OUTPUT AMPLITUDE
vs
FREQUENCY
10
VCC = ± 15 V
9 Gain = 2
RF = 300 Ω
CIN– = 10 pF
8 RL = 150 Ω
VO(PP) = 0.4 V
7
6
No CIN–
5
(Stray C Only)
4
3
2
1
0
100 k
CIN–
300 Ω
VI
300 Ω
_
+
50 Ω
VO
150 Ω
1M
10 M
f – Frequency – Hz
Figure 42
100 M
500 M
OUTPUT AMPLITUDE
vs
FREQUENCY
4
VCC = ± 15 V
3 ^{Gain = –1}
RF = 360 Ω
CIN–= 10 pF
2 ^{RL = 150 Ω}
VO(PP) = 0.4 V
1
0
No CIN–
–1
(Stray C Only)
–2
–3 _VI
360 Ω
–4 ^{56 Ω CIN–}
360 Ω
_
+
VO
150 Ω
–5
–6
100 k
1M
10 M
f – Frequency – Hz
Figure 43
100 M
500 M
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